April 28, 1931.
Dear Doctor Anderson:
We are just beginning to get our results with the dextro- and levorotary phthioic acid and most interesting they are!
Yesterday we killed two rabbits that had received ten doses of the dextrorotary acid.  The omentum was massively thickened in both instances with typical tubercular tissue.  The striking reaction was of monocytes and epithelioid cells; it was a very pure reaction.  In one animal the monocytes seemed to us in our supravital studies to predominate over epithelioid cells.  In the other animal it was the epithelioid cells which did so strikingly.  I am entirely confident that the sections will in both of these animals look like typical tubercular tissue, such as we had from fatty acid No. I.  There were a great many free lymphocytes, so that the sections will probably look just like those from fatty acid No. I in the Monograph.  There was practically no irritation of the serosal lining anywhere and almost not a leucocyte to be seen, so that the reaction was as pure as one could possibly get.
We haw just killed the first animal that had the levorotary acid and we were expecting relatively little.  We got the most extreme, generalized peritonitis -- all the intestines and all the abdominal organs were covered with a thick exudate. The omentum was diffusely thickened, but it was not massively thickened in any place as with the dextrorotary acid.  The cellular reaction is as complex as it can possibly be.  All the serosal cells are irritated to the extreme.  There are leucocytes, monocytes, epithelioid cells, clasmatocytes, and fibroblasts in extreme abundance.  The tissues will look extremely complex, and I think will probably not simulate tubercular tissue at all.  We are just going to start with the second animal and I shall be extremely interested to know if we get the same reaction.  This means, of course, that we must go right to work and study the reaction after one dose and then follow with two doses and three doses.  We have plenty of the material to do this.  With such an extremely irritating substance, the reaction becomes almost too complex to study after the ten day reaction from the standpoint of the supravital reaction.
Are you not astonished that this levorotary acid is so extremely irritating?  We gave it, of course, diluted in nujol as before.
Do you remember telling me that you had sent us in 1928 some of the fat A-5 and my saying that we have never tested it?  We have now found it in the ice-box and will start at once toward its testing.  I am exceedingly sorry that it has been overlooked so long and will let you know what it gives as soon as possible.
Very cordially yours,
Florence R. Sabin.
P.S.  The second animal is exactly like the first, only the reaction is not quite so extreme.  Smears for bacilli are entirely negative and show that there was no puncture of the gut and that the entire reaction was due to the very irritating levorotary acid.
F.R.S.