62 ACTIVITIES OF BACTERIA. 



can thrive in it, the contrary is true. ^ (Compare Table I. ) 

 Since the gases, according to Fermi, are without influence 

 on the activity of the ferment, they must influence the for- 

 mation of ferment. On the contrary, obligate anaerobes pre- 

 ponderately present most beautiful liquefaction of gelatin. 



3. The addition of sugar does not interfere with the 

 growth, but does with the liquefaction of gelatin in the 

 case of many Ijacteria; for example, Bact. vulgare (Proteus 

 vulgaris) (Kuhn, A. H. xiii, 40). 



Auerbach has shown in my Institute (A. H. xxxi, 

 311) that sugar influences, in varying degree, the lique- 

 faction of gelatin by various bacteria. In the instances 

 examined, this checking was dependent upon the fact 

 that no proteolytic ferment was formed in media con- 

 taining sugar, and not that the sugar or acids formed from 

 it interfered with the action of the ferment. 



4. In fluid non-albuminous nutrient media, contain- 

 ing glycerin but no sugar, only a few bacteria produce 

 proteolytic ferment; for example, B. prodigiosum and B. 

 pyocyaneum. Also in peptone bouillon the ferment forma- 

 tion appears less than in peptone bouillon gelatin (Fermi). 



Upon albuminous nutrient media the liquefying bacteria 

 produce bitter-tasting metabolic products; for example, 

 from milk in the case of many varieties (Hiippe). 



An enumeration of the varieties forming trypsin 

 may be omitted, since they are characterized by their 

 liquefaction of gelatin, the other bacterial ferments 

 have been less thoroughly studied. 



Diastatic ferments change starch into sugar. They 

 are recognized in this way: To a thin starch paste contain- 

 ing about 1 % thymol, a culture containing 1 % to 2 % 

 thymol is added. After keeping it in the incubator from 

 six to eight hours, it is tested for sugar with Fehling's 

 solution, when it is recognized by the reduction of the cop- 

 per salt (reddish-yellow precipitate). One may also ex- 

 amine directly potato infusion cultures of bacteria for 

 sugar, in which case 'the sugar is extracted by boiling with 

 alcohol and the extract evaporated to a syrup. It is then 

 dissolved in water and the reaction carried out. 



1 It is questionable whether, in these experiments, equal care was 

 always taken to absolutely exclude oxygen. 



