FERMENTATION 341 



which is alkaline or neutral in reaction, whereas pepsin is 

 only effective in acid solution. 



Amylolytic Enzymes. — A large number of the bacteria 

 excrete ferments of the diastatic class. The organism of 

 cholera, anthrax, glanders, and a number of non-pathogenic 

 varieties possess the power of forming such ferments. They 

 may be demonstrated by their action on starch' paste. A 

 thin starch paste containing 1 per cent, of thymol is com- 

 bined with a culture of the organism, to which 1 to 2 per 

 cent, of thymol has been added. The mixture is then 

 incubated at blood heat for six to eight hours. A little 

 ¥ehling's solution is then added, and the solution heated 

 in a water-bath. If a reduction of the copper solution 

 takes place, resulting in a reddish-yellow precipitate 

 showing the presence of glucose, a diastatic ferment is. 

 present. 



Inversive Enzymes. — The ferments of this class are very 

 uncommon amongst the bacteria. Of a very large number 

 examined only the following gave evidence of producing 

 this ferment : B. megatherium, B, fiuorescens liquefaciens, 

 Vibrio cholercB and Metschnikovii. The enzyme may be 

 demonstrated as follows : A 2 per cent, solution of cane- 

 sugar containing 1 per cent, of phenol is mixed with a 

 culture of the organism also containing 1 per cent, of 

 phenol. After a few hours the solution is tested with 

 Fehling's solution to ascertain if any glucose has been pro- 

 duced. Control tests are always necessary. 



Coagulative Enzymes. — Ferments of the rennet class, which 

 coagulate milk independently of the action of acids, are not 

 wanting amongst the bacteria. 



Duclaux (Comptes Rendus, 1891) and Hueppe {Deutsche 

 Mediz. Wochensch., pp. 48, 49) first pointed out that such 

 ferments are conveyed by many different bacteria, which 

 precipitate the casein in the presence of a weakly acid. 



