98 
Proceedings of Boyal Society of Edinburgh. [jan, 31 , 
disease is rather the result of one or more compounds formed by 
the life-history of a micro-organism, than the mere presence of that 
micro-organism itself. By looking at certain cases in the above 
light, we can well understand why persons suffering with cholera 
die so rapidly. The alkaloid or ptomaine (discovered by Pouchet 
in 1885) which the Comma bacillus secretes or forms is rapidly 
absorbed into the blood, long before the bacillus itself is capable 
of being absorbed by the mucous membrane of the intestine, and 
then into the blood. It is a well-known fact that most micro- 
organisms multiply with great rapidity in the media in which they 
live, and if particular organisms can be destroyed, the harmful 
effects of the products produced by their life-histories will not 
increase, and the disease will soon be at an end. 
Of course, I am fully aware that it must not be supposed that 
because we find in the blood and tissues of man and animals 
(suffering from a contagious disease) certain micro-organisms, that 
these micro-organisms are necessarily the cause, or even indirectly 
the cause, of that disease. Hot until we have obtained by pure 
cultivations, in an artificial sterilised medium, the organisms in a 
perfectly pure state, and then, by an injection into the blood of 
man or an animal of the purified organisms, the disease is repro- 
duced, can we say that a particular disease is the result of the 
life-history of any particular micro-organism. 
It is not my object here to describe the methods adopted by 
physiological chemists to obtain pure cultivations of any given micro- 
organism, although no interpretations can be given of any experi- 
ments unless the experimenter has worked with purified organisms 
obtained by artificial cultivation with all its precautions. 
I wish to detail what appears to my mind the most reasonable 
method for the treatment of those contagious diseases whose “ seat 
of war ” is in the blood itself. I have already had the honour 
of presenting to the Royal Society of Edinburgh a paper “ On 
the Action of Salicylic Acid on Ferments ” (Proc. Roy. Soc. 
Edin ., Ho. 121, pp. 527-530). It was shown in that paper 
that an aqueous solution of salicylic acid (0‘2 grm. of the acid 
in 1000 c.c. of water) was capable of destroying such micro- 
organisms as Mycoderma aceti , Bacterium lactis , and Bacillus 
butyricus ( B . amylobacter). It was found, on a close microscopical 
