32 Proceedings of Royal Society of Edinburgh. [sess. 
has not yet in the case of these organisms been definitely ascer- 
tained. 
We have just seen that each enzyme has its own most appropriate 
temperature, and as the organisms vary as regards their natural food, 
we should expect their enzymes to exhibit great variety as regards 
their capacity of acting on different media. This is very strikingly 
indicated by their action on the different sugars. The yeasts as a 
group are able to attack dextrose, giving rise to what is known as 
the alcoholic fermentation, and they are also able to act on cane 
sugar, which is, however, first converted by an inversive ferment into 
dextrose and levulose. Yet of all the yeasts only three are known 
which are able to ferment milk sugar, the power of converting it into 
dextrose not being possessed by the saccharomyces as a group, al- 
though it is a property very widely distributed among bacteria. Of 
still greater interest is the varying manner in which the same organ- 
ism conducts itself towards different albumenoids. Thus, as a very 
general rule, those organisms which liquefy gelatine are able to co- 
agulate milk, and then peptonise casein which has been separated, but 
some organisms which peptonise gelatine are without action on 
milk. Again, we should expect that those organisms which exhibit 
no enzyme action on gelatine would be inoperative on milk, and 
although this is usually the case there are exceptions to this 
rule. It has been already noted that organisms vary greatly as 
regards the reaction in which they peptonise the milk, and it would 
appear that they even peptonise it in different ways. Although the 
vast majority first coagulate the casein and then dissolve it, certain 
microbes appear to peptonise the casein directly; this would 
indicate that the process in the two cases is not identical.* Very 
striking is the way in which the same organism conducts itself to 
the different albumenoids, gelatin, fibrin, blood serum, and egg 
albumen. One organism is unable to liquefy gelatine, but pep- 
tonises fibrin ; another liquefies the gelatine, but cannot peptonise 
the egg albumen. They exhibit, in this respect, the utmost diversity, 
each having its own special idiosyncrasies. We have thus seen, in 
the course of our investigation, that the enzymes vary in every direc- 
tion as regards the temperature and reaction in which they act, and 
the nature of the medium on which they act. They must, accord- 
* Caneva, TJeber die Schweineseuchen. 
