Contagious and Epizootic Diseases. 43 



firmation, and is rather improbable, considering the assimi- 

 lating power of the animal cell. 



It remains to be noted that other conditions than the 

 presence and absence of air (oxygen) affect the develop- 

 ment and pathogenic power of the bacteria. 



Thns, as the animal linids generally are ancaline{i\ie seci 

 tion of the stomach and contents of the large intestine e 

 cepted), the bacteria that live in them are those adapted -^ 

 an alkaline medium, and are at once debilitated or killed 

 by being placed in an acid medium. Hence, most patho- 

 genic bacteria, taken in with the food, are either killed or 

 rendered harmless by passing through the acid stomach, and 

 those only successfully run this gauntlet that are taken in in 

 the condition of spores, or that pass through during an at- 

 tack of gastric indigestion, when the acid is defective. For 

 the same reason these bacteria require, for their survival 

 out of the body, a medium (soil, fermenting heap) that is 

 naturally alkaline by I'eason of the presence of lime, or by 

 the artiiicial production of ammonia, which is so constant a 

 product of fermentative decomposition. The saturation of 

 the fermenting mass, therefore, with a powerful acid, not 

 only checks the alkaline fermentation but also usually disin- 

 fects the mass if infectious germs are present. 



Light, too, has a marked influence on bacteria growth, 

 the disease-producing forms being especially those that 

 thrive in darkness, while their virulence is more or less im- 

 paired by exposure to sunlight. Hence the great value of 

 light as well as of oxygen as a means of purification and dis- 

 infection. 



Electricity, too, has a potent influence on their develop- 

 ment, though it seems to act differently according to the par- 

 ticular kind of germ and the strength of the electric current. 

 Thus everyone knows the effect of a thunder-storm in rap- 

 idly souring milk, a process which is directly caused by the 

 Bacillus lactis; and the rapid decay of vegetables, and even 



