36 Proceedings of Royal Society of Edinburgh. [sess. 
become exhausted, resorting to the albumenoids present. The 
degree of retardation in the liquefaction of the gelatine will in each 
case depend on the protoplasmic idiosyncrasies of the organism as 
regards the form of nourishment best adapted to its metabolism. 
It is not improbable that an analogous selective action of the 
protoplasm may come into play when organisms are grown anaero- 
bically on gelatine containing grape sugar, and that the absence of 
liquefaction in some of these cases is to be ascribed to this. 
It is not, however, such temporary abeyances of function that I 
wish to consider now, but more permanent changes in the organisms 
themselves as regards this function. The first occasion on which I 
observed the complete loss of the power of liquefying the gelatine 
was in the case of an old gelatine culture of Koch’s cholera bacillus. 
The colonies originating from it presented the usual irregular 
margin and granulated-glass appearance, and, under the microscope, 
cover-glass preparations gave the characteristic comma form, but it 
grew in gelatine without any signs of liquefaction, and in milk no 
separation of the casein took place. On potatoes, which are 
naturally of acid reaction, the growth was either much impaired or 
even completely inhibited, although other samples of cholera grew 
luxuriantly on slices of the same potato. This sensitiveness of the 
organism to acid reaction, when it has lost its enzytne function, will 
be dealt with later. The variety of cholera which had lost its 
enzyme faculty, preserved its new properties for many months when 
cultivated on agar-agar. When grown under other conditions, it 
rapidly regained its power of liquefying the gelatine. Thus, if 
frequently re-inoculated on fresh bouillon, and retained at a tem- 
perature of 25° C., it recovered its former characters in about three 
weeks. Since noting this loss of function in the case of cholera, I 
have had occasion repeatedly to observe the same fact in old 
cultures of many other organisms. Gelatine plates from such tubes 
presented non-liquefying colonies often intermingled with the char- 
acteristic liquefying ones, which had alone been expected. At first 
sight it would appear that the former must be impurities, a view 
which, by preventing further investigation, has no doubt misled 
many who must at some time have observed the same appearances. 
I was able, in such cases, by cultivation under appropriate conditions, 
to cause such aberrant forms to recover their original characters. 
