METEOROLOGICAL CONDITIONS OF SUNSTROKE. 
BY 
W. F. R. PHILLIPS, M.D., 
WASHINGTON, D.C. 
Read before the 
American Climatological Association, Washington, D. C., 
May, 1891. METEOROLOGICAL CONDITIONS OF 
SUNSTROKE. 
By W. F. R. PHILLIPS, M.D., 
WASHINGTON, D. C. 
Sunstroke, insolation, heatstroke, and other more or less 
etiologically significant names are used to denote certain mor- 
bid phenomena which are generally understood to be produced 
or excited by heat, either natural or artificial. The word 
sunstroke is the one most frequently met with in both medical 
and popular literature, and for this reason will be generally 
adopted in this paper. 
In order to avoid any misconception that might arise from 
the use of the term sunstroke as it is generally defined, it is 
necessary to state that throughout this paper it is used in a 
restricted sense, and has reference only to sunstroke as seen in 
temperate climates and to those cases that are apparently ex- 
cited by abnormal meteorological conditions. Those cases 
that are due to artificial heat, such as the heated atmosphere 
of boiler-rooms and the like, although pathologically identical 
with those produced by general atmospheric conditions, can- 
not properly be considered as coming within the purview of 
this paper; but in dealing with very extensive collections 
of statistics it will not be found practicable to exclude all 
such cases from those dependent upon the general condi- 
tion of the weather. It seems also necessary to acknowl- 
edge that the line of demarcation cannot be sharply drawn 
between sunstrokes of purely meteorological causation and 
those of partly or purely artificial origin. Undoubtedly 
many cases of sunstroke have their inception in local sur- 2 
W. F. R. PHILLIPS, 
roundings, but become manifest as such after removal from 
the primary excitant—e. g., a man working in a hot furnace- 
room may, after leaving it apparently well, be overcome under 
atmospheric conditions but slightly abnormal. Cases of this 
and of other sorts, which will doubtless immediately suggest 
themselves to you, render the study of the meteorological 
aspect of sunstroke very difficult and perplexing. 
It seems that, in order to reach any trustworthy opinion as 
to the meteorological conditions influencing or producing sun- 
stroke, it is necessary to assume some arbitrary basis or stand- 
ard as to what shall constitute the presumption that the 
weather was the principal etiologic factor in originating the 
case in question. 
In arriving at the conclusions to which it is the purpose of 
this paper to invite your attention, the author has assumed, 
as the necessary presumptive evidence of meteorological in- 
fluence, the coincidence of the following conditions, viz.: 
that (a) the weather must be noticeably abnormal in some 
particular, (b) the number of sunstrokes must be sufficiently 
great to attract public attention, (c) the sunstrokes must 
not be confined to any particular class, trade, or occupation, 
or to the occupants of any one shop, office, or other struc- 
ture, and (d) they must not be .confined to a particular spot, 
but must occur throughout the locality subjected to the abnor- 
mal weather. Although it may not be strictly correct to use 
the term epidemic in connection with sunstroke, yet when the 
conditions just enumerated are complied with the writer will, 
in order to facilitate reference, speak of such compliance as 
constituting an epidemic of sunstroke. If this explanation 
regarding the use of the term epidemic be kept in mind, no 
confusion or misunderstanding will occur. 
It will, perhaps, not be out of place to close this introduc- 
tion by a brief statement of the generally accepted doctrine 
concerning the meteorological causation of sunstroke. The 
following appear to be the chief points of agreement among 
modern writers : 
The sole efficient cause of sunstroke is heat, either as the SUNSTROKE. 
3 
result of direct exposure to the sun’s rays or to a high atmos- 
pheric temperature in the shade. 
The particular degree of atmospheric temperature that may 
be considered one of great danger is difficult to fix because of 
the great tolerance of heat by persons in perfect health. 
The action of heat is much influenced by the hygrometric 
condition of the atmosphere. A dry, hot air, it is claimed, 
is better tolerated than a moist one at a lower temperature, 
because it favors perspiration, and thereby keeps the body 
cool, while damp air diminishes evaporation and the refrig- 
erating processes of the body. 
Impure air is an important factor, as are also personal 
hygienic conditions and surroundings. 
The injurious effects of heat are primarily exerted upon the 
nervous system. 
In opposition to the importance of high relative humidity 
has been placed the rare occurrence of sunstroke at sea, the 
cases recorded having been stated to have occurred generally 
at night aud between decks where the ventilation was extremely 
bad. 
The special purpose of this paper is to call attention to cer- 
tain facts discovered in the course of an investigation of the 
sunstroke epidemic of August, 1896, and to certain conclu- 
sions that seemed warranted by the facts disclosed. This inves- 
tigation was made by the direction of the chief of the Weather 
Bureau, and the facts ascertained thereby were published in a 
paper contributed to the Monthly Weather Review for Novem- 
ber, 1896, of which the following is a synopsis : 
During the first part of August, 1896, there prevailed over 
a large part of the United States an exceptionally severe and 
prolouged period of hot weather, and during the same period 
there occurred a great many cases of sunstroke. This hot 
weather and the coincident sunstrokes were particularly severe 
in the Middle Atlantic and Central States. In response to a 
circular sent out by the Weather Bureau, information was 
obtained of 2088 deaths from sunstroke; 1817 of these were 
reported by the health officials of the localities in which they W. F. R. PHILLIPS, 
occurred, and the remainder were obtained from what seemed 
fairly trustworthy sources. The cities of Boston, New York, 
Brooklyn, Philadelphia, Baltimore, and Washington furnished 
a total of 1461, and St. Louis and Chicago a total of 310 
deaths. In addition to the number of deaths from sunstroke, 
there were obtained from a number of hospitals and physi- 
cians more or less complete histories of 841 cases of sunstroke. 
A comparison of the meteorological and sunstroke statistics 
showed that: (a) The number of sunstrokes was greatest from 
August 9th to August 12th. (6) The daily mean tempera- 
tures were highest during the same period, and were from 10° 
to 13° above the normal for the month of August, (c) The 
absolute humidity was at its maximum during these four days, 
(d) The relative humidity was above the normal in the Cen- 
tral States and below the normal in the Middle Atlantic States. 
The other recorded meteorologic conditions—i. e., pressure, 
wind, rain, and state of weather—did not show any features 
that could be regarded as significant. 
These facts seemed to warrant the following conclusions : 
(a) That the number of sunstrokes follows more closely the 
excess of the temperature above the normal than it does that 
of any other meteorologic condition. (See Tables A and C, 
and diagram.) (6) That the number of sunstrokes does not 
appear to sustain any specific relation to the relative humid- 
ity, the maximum having occurred in one region with a rel- 
ative humidity above the average, and in the other region 
with a relative humidity decidedly below the average. (See 
Tables A, B, and D, and diagram.) (c) That, although the 
absolute humidity was greatest during the maximum of sun- 
strokes, yet it does not appear that its variations influenced 
the number of cases. (See Table E.) 
The only conclusion enunciated that above conflicts strongly 
with accepted ideas is that regarding the influence of relative 
humidity of the atmosphere. 
Inasmuch as the course of the temperature was the meteor- 
ologic condition that appeared most intimately associated with 
the increase and decrease in the number of sunstrokes, the SUNSTROKE. 
5 
attempt was made to determine what degree of atmospheric 
temperature was necessary or likely to give origin to sun- 
stroke. It was noticed that sunstrokes were reported in 
Boston when the average temperature of the day reached 82°, 
or 13° above the August normal. On the other hand, it was 
observed that the normal August temperature for New 
Orleans was 82°, and that, too, without any sunstrokes. 
Therefore, it was evident that sunstrokes were not excited by 
the same degree of temperature in every locality; and, for 
reasons not necessary to enumerate, it was assumed that each 
particular locality had for its native or acclimated inhabitants 
a special local sunstroke temperature or range of temperature. 
The next step, therefore, was to ascertain, if possible, whether 
this particular local temperature, or climatic sunstroke temper- 
ature, as it may be called, was capable of expression as a 
climatological function. With this object in view, a careful 
examination of the temperatures prevalent during the sunstroke 
period appeared to show that there was empirical evidence for 
adopting as a provisional index to the sunstroke temperature 
of each climate its normal daily maximum temperature. Ap- 
plying this provisional standard to the cases of sunstroke as 
reported in the cities of New York, Boston, Philadelphia, 
and Washington, the following results were obtained: 
In New York City 96 per cent, of the cases occurred with 
daily mean temperatures equal or nearly equal to the normal 
maximum temperature for August, the period in question. In 
Boston and Philadelphia 91 per cent., and in Washington 77 
per cent, of the cases occurred under like conditions of tem- 
perature. In the light of these results, the following work- 
ing hypothesis was proposed: 
Sunstroke becomes imminent during the summer months 
when the mean temperature of any one day or of several con- 
secutive days becomes equal or nearly equal to the normal 
maximum temperature for the period. 
In order that the Association may judge as to the validity 
of the foregoing conclusions and hypothesis, the statistics 6 
W. F. R. PHILLIPS, 
upon which they were based are submitted in the appended 
tables. 
Inasmuch as the foregoing facts and conclusions seem 
resolvable into the generally accepted proposition that heat is 
the sole efficient cause of sunstroke, the chief point of interest 
centres in determining what degree of atmospheric tempera- 
ture is likely to produce in a given community an epidemic of 
sunstroke. I think we may safely assume that while humid- 
ity, relative and absolute, wind, and atmospheric pressure 
may, under special conditions, be very important to a par- 
ticular individual, they are as causative factors of sunstroke 
as a widespread event or epidemic obscured, and sink into 
insignificance in comparison with the overwhelming effect of 
high atmospheric temperature or intense direct insolation. 
Taking this view of the subject, I have endeavored to find, 
by using such statistics for other years as were accessible, how 
far the hypothesis stated could be depended upon as a criterion 
of impending danger from sunstroke, with the result that it 
appears to be a fairly good index for the eastern and central 
parts of the United States. But it is to be remembered that, 
although it embodies certain plausible climatological consider- 
ations, it was evolved simply as an empiricism based upon 
quite a large number of events, and that it does not rest upon 
a satisfactory knowledge of all the factors involved. 
As a matter of possible interest, it may be stated that the 
fatality among the 841 cases previously referred to as reported 
by hospitals and physicians was 16.6 per cent., 140 cases hav- 
ing terminated fatally. It may also be interesting to state 
what appeared to be the influence of alcoholic beverages in 
determining both the incidence and fatality of the affection. 
Of the 841 cases the history of 465 as to the use of alcoholic 
drinks is given as follows: 
Using to excess 
. 140 cases, 
or 30 per cent. 
“ moderately .... 
. 230 “ 
50 
“ not at all 
. 95 
20 “ 
Total .... 
. 465 
100 
History unknown .... 
. 376 
Total .... 
. 841 SUNSTROKE. 
and of the 140 deaths that occurred the history of 70 is given 
as follows: 
Using to excess .... 
41 deaths, 
or 60 per cent. 
“ moderately 
. 22 
30 “ 
“ not at all. 
7 “ 
10 
Total 
. 70 “ 
100 
History unknown 
. 70 
Total 
. 140 W. F. R. PHILLIPS 
Table A.—The Daily Number of Cases of Sunstroke admitted to Certain Hospitals or treated in the practice of 
Certain Physicians from August 1 to 20, 1896, inclusive, together with the Resulting Mortality. 
Places. 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
Total 
cases. 
No. of 
deaths. 
Authority (hospital or physician). 
Manchester, N. H. . . 
... 
1 
i 
1 
Elliott Hospital. 
Albany, N. Y . . . . 
i 
4 
5 
5 
15 
3 
Albany Hospital, 
Rochester, N. Y. . . 
2 
i 
2 
5 
Homoeopathic Hospital. 
Boston, Mass- . . . 
A 
8 
18 
2 
i 
32 
8 
Boston City Hospital. 
New Haven, Conn. 
2 
2 
4 
7 
3 
2 
20 
2 
New Haven Hospital. 
New York, N. Y. . . 
2 
3 
9 
5 
12 
15 
49 
78 
106 
64 
9 
5 
357 
62 
Hudson Street, Roosevelt, and New York hospitals. 
Brooklyn, N. Y.. . . 
2 
4 
8 
5 
11 
26 
32 
11 
2 
2 
103 
22 
St. John’s, St. Mary’s, and Brooklyn hospitals. 
New Brunswick, N. J. 
1 
1 
3 
5 
2 
Drs. Williamson and Smith. 
Philadelphia, Pa. . . 
i 
9 
11 
13 
8 
22 
30 
34 
21 
13 
2 
164 
16 
St. Agnes’, Episc., Med.-Chir.. and Hahn’n hosps. 
Washington, D. C.. . 
l 
1 
2 
3 
2 
o 
1 
3 
2 
1 
i 
22 
7 
United States Government Hospital for Insanp 
— 
— 
— 
— 
— 
— 
— 
— 
— 
— 
— 
— 
— 
— 
— 
— 
— 
— 
Garfield, Providence, and Freedman hospitals. ’ 
Middle Atlantic States 
2 
5 
22 
22 
39 
31 
97 
154 
202 107 
28 
14 
2 
... 
Pittsburg, Pa . . , 
1 
... 
1 
2 
2 
S. S. Hospitals. 
Cincinnati, Ohio . . 
3 
2 
2 
4 
2 
8 
4 
9 
7 
1 
2 
3 
i 
48 
5 
U.S. Marine Hosp., St. Mary’s, and Cincinnati hosps. 
Columbus, Ohio. . . 
1 
1 
2 
St. Francis’ Hospital. 
Cleveland, Ohio. . . 
4 
4 
i 
9 
2 
St. Alexis’, St. John’s, and Huron Street hospitals. 
Detroit, Mich. . . . 
1 
1 
2 
United States Marine Hospital. 
Holland, Mich. . . . 
i 
i 
2 
Dr. Henry Kremeis. 
Chicago, III 
2 
i 
i 
l 
6 
3 
i 
i 
2 
1 
19 
4 
St. Luke’s, Mercy, and Michael Reese hospitals. 
Springfield, 111. . . . 
1 
l 
2 
City Physician, Wabash Emp. Hospital. 
Louisville, Ky . . . 
2 
i 
3 
i 
2 
9 
City Hospital. 
Cairo, 111 
i 
1 
Dr. W. F. Grimsted. 
Hannibal, Mo. . . . 
i 
3 
... 
i 
5 
i 
Drs. R. H. Godin, S. Q. Smith, P. L. Kabler. 
Columbia, Mo. . . . 
... 
.. 
i 
1 
Dr. W. A. Norris. 
Kansas City, Mo. . . 
i 
2 
1 
4 
i 
Drs. W. S. Wheeler, L. A. Berger, C. L. Hall. 
Des Moines, Iowa . . 
1 
1 
Dr. F. L. Wells. 
St. Paul, Minn. . . . 
i 
i 
2 
i 
City and County Hospital. 
Central States . . . 
6 
7 
4 
9 
8 
16 
17 
15 
it 
2 
1 
6 
5 
l 
l 
Raleigh, N. C. . . . 
l 
1 
Rex Hospital. 
Charleston, S. C. . . 
i 
1 
City Hospital. 
Mobile, Ala 
i 
1 
Dr. J. A. Abrahams. 
Dallas Tex 
i 
i 
l 
3 
Parkland Hospital, 
Palestine, Tex. . . . 
1 
1 
i 
Dr. J. M. Colley. 
Grand total . . . 
1 
...1 6 
10 
9 
31 
30 
56 
48 
*112 
166 
204 
108 
34 
19 
2 
l 
l 
3 
841 
140 SUNSTROKE. 
Places. 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
1 
i 18 
1 
19 
20 
Authority. 
Massachusetts, Connecticut, Rhode 
Island, New York, Pennsylvania, 
Maryland, District of Columbia, 
4 
11 
11 
28 
107 
204 
274 
264 
10S 
37 
5 
4 
2 
1 
1 
Newspaper clippings, health 
and Virginia, 
oincers' reports, 
special re- 
ports, physicians, and others. 
Ohio, Kentucky, Tennessee, Indi- 
ana, Illinois, Michigan, Wisconsin, 
Minnesota, Iowa, Missouri, and 
1 
\ 
1 
5 
5 
14 
16 
13 
50 
100 
58 
14 
3 
1 
2 
1 
1 
... 
(The information from which 
this table is compiled is far 
from complete.) 
Oklahoma. 
Total 
1 
5 
9 
25 
27 
41 
157 
304 
832 
278 
111 
38 
5 
6 
1 
2 
1 
2 
Table C.—The Mean Temperature of 
EACH 
Day 
AT 
Certain 
Selected 
Stations during 
THE 
Sunstroke Epidemic 
OF 
August 3 to 
18, 
1896, INCLUSIVE. 
Places. 
3 
4 
5 
6 
7 
8 
I 
9 
1 
10 
ii 
12 
13 
14 
15 
16 
17 
18 
Normal. 
Normal 
Maximum. 
Albany, N. Y 
72° 
78° 
82° 
83° 
82° 
82° 
82° 
84° 
83° 
82° 
77° 
76° 
75° 
74° 
69° 
64° 
71° 
80° 
Boston, Mass 
71 
78 
72 
65 
77 
75 
82 
86 
82 
82 
76 
71 
67 
74 
72 
68 
70 
78 
New Haven, Conn 
71 
77 
80 
72 
77 
81 
82 
84 
83 
84 
82 
7 
1 
72 
73 
69 
64 
70 
78 
New York, N. Y 
74 
77 
80 
82 
80 
82 
82 
84 
85 
84 
81 
75 
74 
73 
68 
65 
73 
80 
Philadelphia, Pa ... 
77 
79 
82 
86 
84 
86 
87 
84 
87 
87 
85 
77 
79 
78 
74 
71 
74 
82 
Washington, 1). 0 
78 
8(1 
83 
88 
87 
84 
87 
84 
84 
86 
82 
78 
77 
79 
73 
71 
75 
84 
Chicago, 111 
77 
82 
84 
79 
77 
87 
83 
86 
81 
73 
72 
78 
76 
72 
68 
65 
71 
78 
St. Louis, Mo 
82 
86 
88 
90 
91 
91 
90 
84 
86 
82 
79 
81 
86 
77 
72 
72 
77 
86 
Cincinnati, Ohio .... 
78 
78 
81 
85 
76 
84 
85 
84 
82 
78 
80 
78 
82 
76 
68 
70 
75 
84 
Charleston, S. C 
84 
80 
83 
82 
82 
85 
87 
86 
84 
82 
84 
82 
80 
84 
86 
80 
81 
87 
Jacksonville, Fla 
86 
84 
82 
83 
84 
84 
86 
86 
86 
84 
85 
83 
84 
84 
84 
86 
82 
90 
New Orleans, La 
82 
86 
86 
84 
84 
81 
78 
82 
82 
86 
84 
82 
80 
82 
85 
87 
82 
88 
Table B.—The Daily Number of Deaths from Sunstrokr Occurring in Certain Regions between August 1 
and 20, 1896. inclusive. W. F. R. PHILLIPS, 
Places. 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
Normal. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Albany 
0 
+3 
— 7 
— 5 
+ 9 
+8 
+4 
— 4 
— 3 
— 5 
+ 1 
— 2 
— 6 
+ 8 
—20 
+ 5 
76 
Boston . 
— 2 
-9 
+ 3 
+19 
+ 9 
—3 
—1 
— 5 
—12 
— 5 
+ 1 
+16 
+ 14 
+ 7 
—15 
—11 
75 
New Haven . 
— 1 
—1 
— 8 
+15 
+13 
—3 
—1 
— 1 
— 7 
— 7 
— 5 
+ 15 
+ 9 
— 9 
—11 
79 
New York . 
0 
+2 
— 9 
+12 
+ 7 
-f 4 
+4 
—10 
— 4 
—10 
— 7 
+17 
+15 
+12 
2 
+10 
74 
Philadelphia 
— 9 
0 
— 2 
+ 2 
+ 1 
—3 
—2 
—12 
—14 
—20 
— 6 
+ 6 
+ 8 
+10 
—30 
—16 
72 
Washington 
— 9 
0 
+ 4 
— 8 
— 7 
—8 
—7 
— 8 
— 6 
—13 
+12 
+ 4 
0 
+ 2 
—12 
-18 
76 
Chicago 
— 3 
—3 
— 6 
+12 
+14 
+1 
+5 
+ 7 
— 1 
+18 
+16 
+12 
+ 6 
+ 8 
—14 
— 8 
68 
St. Louis 
+ 1 
+4 
— 1 
— 9 
— 3 
—1 
—7 
+ 3 
+ 3 
+18 
+ 9 
+ 9 
+11 
+22 
+19 
+23 
67 
Cincinnati . 
— 1 
+3 
+ 1 
+ 7 
+15 
+9 
+7 
+ 3 
0 
+ 4 
+ 6 
+ 5 
+ 5 
+ 7 
—10 
—10 
65 
Charleston . 
+ 4 
+6 
4- 
0 
— 1 
+1 
—5 
— 3 
— 1 
— 1 
+ 1 
0 
— 1 
+ 1 
+ 4 
82 
Jacksonville 
—13 
+7 
+ 3 
— 1 
— 3 
—6 
—8 
—11 
— 4 
— 8 
+ 3 
— 5 
— 1 
— 3 
— 7 
— 3 
81 
New Orleans 
— 2 
+5 
—11 
— 5 
— 1 
0 
+1 
+ 3 
— 9 
—13 
— 3 
0 
+ 3 
0 
— 7 
— 6 
79 
Table E.—The Daily Absolote Humidity (grains per cub. ft.) at Certain Stations from August 3 to 13,1896, 
inclusive. 
Places. 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
Normal. 
Boston . 
6.6 
7.0 
6.6 
6.1 
8.5 
7.5 
8.8 
8.0 
8.0 
8.5 
7.0 
7.0 
6.4 
6.6 
5.0 
4.4 
5.6 
New York . 
6.6 
7.5 
7.7 
8.5 
8.5 
8.5 
9.4 
8.0 
8.8 
8.0 
7.5 
8.0 
7.5 
8.0 
5.6 
5.2 
6.1 
Philadelphia 
6.2 
7.5 
8.0 
9.1 
8.5 
8.5 
9.1 
8.2 
8.0 
7.2 
8.0 
8.0 
7.5 
8.0 
3.8 
4.2 
6.1 
Washington 
7.0 
8.0 
9.1 
8.5 
8.2 
8.5 
10.0 
7.5 
8.5 
8.5 
8.0 
8.0 
8.0 
8.5 
5.6 
4.7 
6.6 
Chicago 
6.4 
7.2 
7.5 
8.0 
8.5 
8.5 
9.4 
8.8 
8.0 
7.5 
7.2 
7.5 
6.8 
6.1 
4.9 
4.1 
5.4 
St. Louis 
7.5 
8.8 
9.1 
8.5 
9.1 
9.4 
8.5 
8.5 
9.1 
8.5 
8.0 
8.2 
8.5 
8.5 
7.5 
7.5 
6.1 
Cincinnati . 
6.6 
7.2 
7.5 
8.0 
8.0 
8.5 
8.8 
8.5 
7.5 
7.0 
7.7 
7.5 
7.5 
7.0 
4.1 
4.4 
5.7 
Charleston . 
8.8 
9.6 
9.6 
9.1 
9.4 
9.6 
9.1 
9.6 
9.6 
9.6 
9.1 
9.6 
9.1 
9.4 
9.4 
9.1 
8.8 
Jacksonville 
8.5 
9.1 
9.1 
9.1 
8.8 
8.5 • 
8.5 
8.2 
8.5 
8.5 
9.4 
8.8 
9.1 
8.8 
8.5 
9.1 
8.5 
New Orleans 
9.1 
8.8 
8.5 
8.5 
9.1 
8.0 
8.5 
8.8 
8.0 
7.5 
9.1 
8.5 
9.1 
8.8 
9.1 
9.1 
8.5 
Table D.—The Departure of the Daily Relative Humidity from the Normal at Certain Stations from 
August 3 to 18, 1896, inclusive. SUNSTROKE. DISCUSSION. 
DISCUSSION. 
Dr. Babcock referred to various factors in the production of sun- 
stroke, e. g., the fact that the individual may be suffering from a cir- 
culatory disease, or that he cannot be dissociated from habits, not 
only of drinking alcohol, but of taking iced drinks. 
Dr. Solly : I am surprised to learn from Dr. Phillips’s table that 
there was an increase of sunstroke, with, at the same time, a decrease 
in the relative humidity. Sunstroke is certainly less common during 
hot weather in dry climates than in damp ones. I have personally 
observed this to be the case both in Egypt and in Colorado. Persons 
are occasionally prostrated by the direct burning rays of the sun, but 
sunstroke—that is, sun apoplexy—is practically unknown in these 
countries, while, on the other hand, in humid England it occurs not 
infrequently and at much lower temperatures than it does in the com- 
paratively drier atmospheres of the United States. The influence of 
alcoholism in predisposing to sunstroke is evidenced by the fact that 
in England, where the laborers always drink freely of some form of alco- 
holic beverage during harvest, there are more sunstrokes in the districts 
where beer is used than where the weaker liquor of cider is consumed. 
Dr. Brastnan : Dr. Phillips’s paper and charts are of great interest 
and value from a clinical as well as from a meteorological standpoint. 
They appeal to me with especial force, as I was in New York last 
summer throughout the hot period which he describes. Dr. Phillips 
considers that the high temperature was the chief factor in the great 
mortality of that time; it seems to me that we should rather say the 
continuous high temperature. Sunstrokes seldom occur unless the 
thermometer remains high for several days in succession. During 
the week of uninterrupted heat last summer the number of sunstrokes 
increased from day to day, but dropped at once to very low figures 
with the first fall in the temperature. Had we had one cool day in 
the middle of that week I believe that the sunstrokes would have 
practically ceased, and several days of hot weather would have been 
necessary before the number would have risen again to high figures. 
I have spent the summer in New York for the past twelve years, 
and have noticed that two or three hot days are borne with tran- 
quillity; but at the end of a week our power of resistance is so les- 
sened that a feeling of desperation comes over one, and it seems 
impossible to bear the hpat any longer. It is under such circum- 
stances that men resort to stimulants, which operate to increase the 
hurtful effect of the temperature. The majority of the cases treated 
in Bellevue Hospital last summer had been taking some form of 
alcohol at the time they were struck down, and such cases usually 
resulted fatally. SUNSTROKE. 
Dr. Phillips : In reference to what Dr. Brannan said regarding 
continuous high temperature, I agree entirely with him. In speaking 
of the matter I meant to intimate that the atmospheric temperature 
must be high and continue high for some considerable period—two or 
more days at least—and I am very giad that he has called attention 
to this point, in order that it may be brought out prominently. The 
human body is so constituted that it can stand a very high degree of 
atmospheric temperature, provided the temperature be not of too long 
duration. Experimenters have endured for a few minutes, without ap- 
preciable ill effect, temperatures of about 260° F. Of course, if during 
this hot spell the temperature had dropped to nearly normal for even 
a day we should probably have had considerably fewer sunstrokes. 
I have no doubt that many of the cases of sunstroke are the result 
of indulgence to excess in alcoholic drinks, and during very hot 
weather I think the use of alcohol as a beverage in any form is to be 
condemned, and this appears to be the opinion of all physicians that 
have observed or studied the subject of insolation. 
Now, concerning the question of atmospheric humidity: 
By absolute humidity is meant the real amount of water existing as 
vapor in a unit volume of air. This amount is, in English measures, 
usually stated as grains of water per cubic foot of air. 
By relative humidity is meant the ratio that the amount of vapor 
actually present bears to the amount required to saturate the space at 
the given temperature. Relative humidity is usually stated as per- 
centage. 
The amount of vapor required to saturate a given space will depend 
upon the temperature. For example, a cubic foot of air at 50° F. will 
require for saturation 4.09 grains of vapor, and if we raise the tem- 
perature to 98° F. it will take 18.69 grains to effect saturation. Thus 
a cubic foot of air at 50° F. saturated with moisture would have a 
relative humidity of 100 per cent.; but if its temperature was raised to 
98° F. it would have a relative humidity of only 22 per cent. Con- 
versely, a cubic foot of air at 98° F., the relative humidity of which 
was 22 per cent., if cooled to 50° F., would have a relative humidity of 
100 per cent. In both illustrations the actual weight of vapor or 
absolute humidity remains unchanged. Absolute humidity is a state- 
ment of a physical condition independent of any other conditions; 
whereas relative humidity is a statement of a relation that, to be 
rationally understood, requires that we shall know both the tempera- 
ture and the absolute humidity. Relative humidity is not a meteor- 
ologic element; it is simply a questionable convenience, so far at least 
as medical climatology is concerned. The use of these two terms, 
relative and absolute humidity, is very apt to lead to confusion in the 
minds of those who meet them for the first time, and it seems to me 
that a new term might be introduced to describe one of these condi- DISCUSSION. 
tions—that is, a term that would not likely be confused with the 
other. 
In New York the absolute humidity on August 9th was 9.5 grains 
of moisture to the cubic foot; on the 12th it was only 9 grains. For 
some reason that I do not understand, it declined before the tempera- 
ture. I did not illustrate the absolute humidity on the chart, but if 
we were to draw a line to indicate it it would about parallel the line 
that indicates the temperature, however, commencing to fall a little 
before that line does. 
Concerning the influence of atmospheric humidity upon heat loss, the 
subject is yet one for us to determine. Moist air has greater capacity for 
heat than dry air at the same temperature; but how does this affect our 
comfort? If it imparts more heat to us, conversely it must abstract 
more heat from us. It is true that we feel heat or cold more acutely 
when the atmosphere is relatively damp ; but may this not be caused 
by the effect of moisture upon cutaneous sensations in general rather 
than any real action of moisture as a thermolytic factor ? A dry skin 
is not as appreciative to tactile sensations as a moist one. Of course, 
we can assume extreme cases of an atmosphere saturated with moisture 
at a temperature of the human body, and then there is no question of 
the effect of the humidity; but in nature we will not meet in this 
country with any instance approximating such a state of affairs. In 
the hottest weather the humidity will never be such that it will inter- 
fere with the evaporation of all the perspiration excreted under normal 
conditions of exercise and rest. 
In regard to Dr. Babcock’s remarks, I did not refer to iced drinks, 
because that aspect of the subject was not included in my statistical 
information. Of course, a great many people suffer from sunstroke 
because of weak circulatory systems or other diseased conditions ren- 
dering them unable to resist the occasional excessive high tempera- 
tures of our summers. Any habit or practice that tends to impair 
health would doubtless, in excessively hot weather, contribute to the 
incidence of sunstroke in the individual indulging therein. 
During the hot weather of August there was one feature of the 
temperature with which I have since been struck, and which may be 
of considerable importance in the causation of sunstroke epidemics, 
that is, that during the prevalence of the epidemic the night tempera- 
tures did not fall below 75° F. I think this high night temperature 
had a particularly bad effect; if we could only have gotten a little 
relief for but a few hours of the night, perhaps we would have stood 
the high temperature of the day very much better and for a much 
longer time. This point has been emphasized in my estimation by 
the following facts : 
Among the statistics that were gathered were accounts of about 
seventeen cases of sunstroke in Arizona and California (these facts SUNSTROKE. 
were furnished by the health officials of the different communities 
and are authentic). Most of the cases occurred in July, 1896, during 
which month the Pacific and Rocky Mountain States suffered severely 
from a prolonged spell of hot weather. In Arizona and California 
temperatures of 108° and 110° F. were recorded during the day, and 
frequently the night temperatures did not fall below 75° F. It was 
upon these occasions that most of the above cases occurred. There- 
fore, I think in order to produce a sunstroke epidemic it is necessary 
that the night temperatures be high as well as the day temperatures. 
These considerations suggest, so far as the etiology of sunstroke is 
involved, the probable importance of diurnal temperature range, and 
the climatologic conditions that favor the same and which, perhaps, 
account for the relative infrequency of sunstroke in such climates as 
Colorado and Egypt, where, owing to the relative dryness of their 
atmospheres, there are very few clouds to interfere with terrestrial 
radiation, and as a consequence the temperature always falls very 
much after sunset. As an indirect agent in the climatologic distribu- 
tion of sunstroke, humidity and its relation to temperature may thus 
be of great significance. ■ 
As Dr. Solly has remarked, there are two perhaps distinct causes ot 
sunstroke—one, the effect of intense direct insolation, and the other 
the effect of high atmospheric temperature. I think the former va- 
riety rare, and the latter the more common in the temperate zones. 
What I have called sunstroke in this paper might with more propriety 
be denominated heatstroke, but I have used the former term because 
it is the more common.