40 BACTERIOLOGY. 



bring about the alteration so slowly that it is concealed 

 by the simultaneous production of alkali. Among the 

 acids formed by bacteria, besides carbon dioxid, we have 

 lactic, acetic, butyric, proprionic, and formic ; and fre- 

 quently there is also produced ethyl alcohol, aldehyd, 

 and acetone. 



The lactic acid formed by the action of different bac- 

 teria on carbohydrates may be either dextrorotatory or 

 laevorotatory, or almost equal quantities of both forms 

 may be present and the mixture be optically inactive. 



PRODUCTS OF BACTERIA. As stated, bacteria that 

 produce disease are known as pathogenic. They induce 

 disease by their poisonous action upon the tissues in 

 which they are located. The materials of which cer- 

 tain species of bacteria are constructed, and the products 

 of growth of certain others, are of the greatest import- 

 ance in their relation to animal and human pathology. 

 Particular species, while not eliminating soluble poisons 

 as a product of metabolism, are nevertheless themselves 

 built up of poisonous proteids, or of proteids with 

 which toxic materials are so intimately associated that 

 they can only be isolated by the most refined and elabo- 

 rate chemical manipulations. Others produce in the 

 course of their growth soluble poisons that can readily 

 be separated, by very simple methods, from the bacteria 

 that produced them. The proteid matters making up 

 the bodies of many species of bacteria, even those -not 

 conspicuously pathogenic, have been shown by Buchner 

 to induce disease when isolated and injected into the 

 tissues of animals ; in some cases causing only rise of 

 body-temperature, in others acute inflammatory proc- 

 esses with pus-formation. To such proteids Buchner 

 has given the name bacterial proteins. 



