136 BACTERIA. 



tivated on starch, there came a period at which it generated 

 a diastatic ferment, which could be separated from the solu- 

 tion, and which alone, and without any direct intervention 

 of the protoplasm, could bring about a transformation of 

 starch into sugar i.e., a secondary separable diastatic func- 

 tion had been developed, in addition to the primary digestive 

 function of the organism. When taken back to the gelatine 

 from the starch, the organism had lost its power of liquefy- 

 ing gelatine ; but this again it regained, after being again 

 cultivated, through a series of generations, on gelatine. 



It is quite possible that this may be a somewhat too strong 

 statement of Lauder Brunton's and M'Fadyean's position. It 

 may be that they maintain only that the organism when 

 grown on starch produces the diastatic ferment, whilst when 

 on albumen it forms a peptonizing substance. It may be 

 merely a temporary modification just as under analagous 

 conditions, the cholera bacillus when grown on sugar produces 

 butyric acid; whilst when grown on albumen it forms 

 ptomaines. 



It is thus evident that special forms of fermentation require 

 that, in addition to a special kind of protoplasm, there shall 

 be a special nutrient material a fact that explains some of 

 the different results that have, from time to time, been 

 recorded. The yeasts, as we have seen, are capable of fer- 

 menting dextrose and of producing a substance, invertin, by 

 which the saccharose, or cane sugar, is converted into dex- 

 trose and levulose both fermentable substances. Wood 

 points out that only three yeasts are known that are able to 

 ferment milk sugar directly, although many of the bacteria 

 are able to invert and bring about its fermentation. He says 

 that 



" Of still greater interest is the varying manner in which the same organism 

 conducts itself towards different albuminoids. ... As a general rule, those 

 organisms which liquefy gelatine are able to coagulate milk, and then 

 peptonize casein which has been separated ; but some organisms which 

 peptonized gelatine are without action on the milk, and some that are 

 inoperative on gelatine peptonize milk, though this is exceptional " ; and he 

 further says that even the manner in which " milk is peptonized is subject to 

 considerable variations, and that, although the vast majority first coagulate 

 the casein and then dissolve it, certain microbes seem to peptonize the 

 casei- directly. . . . Very striking is the way in which the same organism 

 con % s itself to the different albuminoids, gelatine, fibrin, blood-serum, 

 -.lbumen. One organism is unable to liquefy gelatine, but pep- 

 ;rin ; another liquefies the gelatine, but cannot peptonize the 



