CHAP, vii] CHEMISTRY OF BACTERIA 123 



tetanus (anaerobic), bacillus enteritidis sporogenes (anaero- 

 bic), bacillus butyricus (anaerobic), Koch's cholera vibrio, 

 vibrio of Tinkler ; actinomyces, aspergillus and penicillium, 

 &c. Some liquefy the gelatine extremely slowly, the liquefied 

 gelatine being more of the consistency of thick syrup, e.g. 

 bacillus of swine-erysipelas and of Koch's mouse-septi- 

 CEemia. 



In the case of all aerobic microbes, which have the power to 

 liquefy (peptonise) nutritive gelatine, this power is intimately 

 bound up with a free supply of oxygen (air) ; it proceeds from, 

 and is conspicuous on the surface, it is greatly retarded when 

 air is excluded, and in some cases is only noticed where the 

 growth occurs on the surface in contact with air. 



But there are a good many microbes which do not 

 peptonise, do not liquefy the gelatine : all the species forming 

 the group of bacilli causing hsemorrhagic septicaemia in 

 the rodents : bacillus of fowl cholera, of swine fever, of fowl 

 enteritis, all varieties of bacillus coli, bacillus of typhoid 

 fever, bacillus of "Wildseuche," &c. — all or nearly all (a few 

 species excepted) species of streptococci, a number of chro- 

 mogenic cocci, &c. 



2. Another widespread manifestation is that of producing 

 acid or alkali ; when growing in a neutral medium, as in 

 Petruschki's neutral whey, of turning this acid or alkaline, as 

 the case may be, the latter being more often met with than 

 the former (Petruschki, Centfalbl. f. Bakt. and Parasit. 

 1889 and 1890.) 



Buchner has first suggested a method which is very easy 

 of employment, and which demonstrates conspicuously 

 whether a microbe during its growth produces acid or alkali 

 or is neutral — viz., by mixing with the nutritive medium, 

 before steaming, a small amount of litmus tincture, 

 sufficient to stain it bluish. The nutritive gelatine, slightly 



