28 
Proceedings of Royal Society of Edinburgh. [sess. 
processes of digestion in the higher animals. Upon the view which 
we take as to its origin and meaning will depend the standpoint from 
which we regard many important physiological and pathological 
questions. 
Although Duclaux and Hueppe, in their investigations on milk, 
had suggested the probable existence of soluble ferments, H. Bitter 
in 1887 first furnished rigorous proof that bacteria produce enzymes 
separable from the organisms which form them. He managed to 
kill the organisms by sterilisation at 60° C. without materially 
destroying their products, and in this way demonstrated that two 
organisms, when grown on gelatine, produced enzymes which were 
able, apart from the organism, to liquefy gelatine and peptonise 
albumen. Sirotinin, in an investigation carried out in Eliigge’s 
laboratory, noted incidentally, that culture fluids which had been 
freed from organisms by means of Chamberland’s porcelain filter, 
still retained the power of liquefying the gelatine. Brunton and 
Macfadyen have, more recently, communicated the same fact for 
another organism, and have stated in addition that when grown on 
starch a diastatic ferment was there produced. My own experiments 
were undertaken, not for the purpose of demonstrating the existence 
of such enzymes, but if possible to investigate more minutely their 
properties. Bor this purpose the four organisms which form what is 
known as the cholera group — Koch’s cholera bacillus, Deneke’s cheese 
bacillus, Finkler’s cholera nostras bacillus, and Miller’s bacillus — were 
selected. These organisms exhibit in all directions a most striking 
similarity, and the point which I wished to investigate was whether 
their enzymes could be shown to differ in any way. The reaction 
in which they would continue to act offered itself as the most con- 
venient test. The method of experimentation pursued was as fol- 
lows: — A tube containing 20 c.c. of sterilised milk was taken, and to 
it a certain quantity of acetic acid was added. The fluid was shaken, 
and then delivered, by means of a sterilised pipette, in equal quan- 
tities, into four test tubes. To each of these 1 c.c. of the sterilised 
products of one of the organisms was added, and the result noted. 
By making a series containing varying quantities of acid the effect 
on the enzyme action was ascertained. The cholera enzyme was 
found to be most sensitive towards acid reaction, even very small 
quantities inhibiting its activity. Deneke came next, while 
