[Reprinted from The Medical News, September 28, 1895.] 
THE USE OF THE A U T 0 C L A 1/E FOR STERI- 
LIZING N UT R IE NT G E LATI N. 
By WYATT JOHNSON, M.D., AND J. E.' LABERGE, M.D., 
OF MONTREAL, CAN. 
\From the Laboratory of the Board of Health of the Province 
of Quebec.} 
An impression seems to exist in many bacteriologic 
laboratories that the sterilization of nutrient gelatin by 
means of the autoclave is impracticable, owing to the 
tendency of this medium to lose its power of setting 
firmly when exposed to a temperature above the boil- 
ing point of water. Our experience has shown the con- 
trary to be the case, and the results obtained by a single 
sterilization in the autoclave have been fully as satis- 
factory as those obtained by fractional sterilization at 
ioo° C. on successive days, so that we now employ the 
autoclave by preference to avoid delay and uncertainty. 
The steam-pressure employed is 3/4 of one atmosphere 
(equal to H5°C.), saturated steam for fifteen minutes, 
after the gelatin has been filtered and filled into tubes. 
In a series of comparative tests in which half of the 
nutrient medium was prepared by fractional sterilization 
in an Arnold sterilizer, that prepared in the autoclave 
was equally transparent, retained the desired degree of 
alkalinity (usually 2 per cent, acid to phenolphthalein), 
and remained firm in plates or roll-tubes at a tempera- 
ture of from 240 to 250 C. In no case have we had 
any spontaneous growth in the tubes after this steriliza- 
tion. 2 
We claim no priority for these observations, as the 
autoclave at 105° C. seems to have been employed for 
some years in several French laboratories for sterilizing 
gelatin,1 though this fact does not appear to have be- 
come as generally known as it might be. In the labora- 
tory of the Board of Health of the Province of Quebec 
attention was first attracted by the fact that some gela- 
tin, sterilized in the autoclave through a mistake, re- 
tained its power of setting. In our experience a tem- 
perature of 105° C. has not always been sufficient to 
insure perfect sterilization. 
With reference to the temperature we employ, it may 
be well to mention that the test-tubes and small bottles 
which we use are made of very thick glass, so that the 
heat penetrates slowly. In working with thinner ones 
a lower pressure or a shorter time may be found to give 
the best result. We have employed gelatin giving a firm 
jelly, as considerable difference exists between the dif- 
ferent brands in respect to their melting-points.