236 BACTERIA PATHOGENIC TO MAN 



COAGULATED SERUM. The serum is not liquefied. On this medium 

 grayish, uncharacteristic colonies are developed. 



MILK coagulates in from four to ten days at 20 C., and in from one 

 to four days at 37 C. Coagulation is aided by the addition of pep- 

 tone; it is prevented by constant addition of alkalies. The acids 

 formed are lactic, acetic, formic, and succinic acids. Coagulation is 

 due principally but not altogether to acids. A ferment is produced 

 which is capable of causing coagulation in the presence of lime 

 salts, especially in acid solutions. It is evident also that the nature 

 of this coagulation is more closely related to coagulation fermentation 

 than to simple acid fermentation, from the fact that colon coagulation 

 forms a compact mass which is difficultly soluble in alkalies, and 

 contains much insoluble residue; and further, that in serum coagulated 

 by colon bacilli a proteid body corresponding to fermentation albumin 

 is found. 



In addition to albumose it has been shown that milk serum, after 

 colon coagulation, contains a substance possessing the reaction of pep- 

 tone, which is not contained in the original milk. Similar albumin 

 cleavage products are also formed in cultures of bacillus coli in sugar- 

 free ascitic fluid; it cannot be assumed, therefore, that colon acidification 

 of milk, as such, produces this proteolysis. The colon bacilli also differ 

 from typhoid bacilli in that their action on milk-sugar is more intense, 

 and, since they can grow in greater acidity, more lasting. The dif- 

 ference, therefore, is quantitative rather than qualitative. 



Chemical Activities. BEHAVIOR TOWARD CARBOHYDRATES. In cul- 

 tures of colon bacilli many carbohydrates, especially sugars, become 

 fermented. Among these are: 



Hexoses, C fi H 12 O 6 (glucose, mannose, fructose, galactose). 



Pentoses, C 5 H 10 O 5 (arabinose, xylose). 



Binoses, C 12 H 22 O lt (saccharose, lactose, maltose, melitose). 

 Also the higher alcohols: 



Hexatomic alcohol (mannit, dulcit, sorbit). 



Pentatomic alcohol (erytherit). 



Triatomic alcohol (glycerin). 



The varieties included under colon bacilli vary in their action on 

 some of the sugars; some ferment cane-sugar, others do not. All fer- 

 ment glucose. For fermentation they require nitrogenous substances 

 which can be utilized as food by the bacteria, a suitable temperature 

 (best at 30 to 35 C.), absence of deleterious substances. 



The products derived from the splitting of the carbohydrates are 

 as follows: From glucose, saccharose, arabinose, and galactose there 

 is mainly produced /cpi>o-lactic acid along with 5 to 25 per cent of 

 dextro-lactic acid; mannit, on the contrary, yields only /i>o-lactic acid. 

 The lactic acid formed, however, corresponds to only one-half the 

 quantity of sugar present. The by-products are : gaseous compounds, 

 alcohol, succinic, acetic, and formic acids. The most important fermen- 

 tation products, both qualitatively and quantitatively, are produced 

 from grape-sugar, probably, according to the following reaction: 



