28 CLINICAL BACTERIOLOGY. 



among the products of fermentation. Not only grape-sugar, 

 but also numerous other varieties of sugar (lactose, galactose, 

 arabinose, etc.) may undergo fermentation in consequence of 

 the activity of certain kinds of bacteria. Fats are split up 

 into fatty acids and glycerin. Much study has been devoted 

 to the changes that albuminoid substances undergo as a re- 

 sult of the activity of bacteria, and that, accordingly as 

 more or less fetid gases are generated, are designated 

 putrefaction or decomposition. From the aromatic group 

 of the albumin-molecule there result aromatic amidoacids 

 (tyrosin, amidophenylpropionic acid, etc.) and certain ben- 

 zol-derivatives, which impart to some bacterial cultures and 

 to the feces their characteristic offensive odor (phenol, indol, 

 skatol, etc.). 



From the group of fatty bodies of albumin the bacteria 

 form, in addition to fatty acids, oxyacids, and amidofatty 

 acids (leucin, glycocol, alanin), a large number of organic 

 toxic bases, which are designated ptomains, and for our 

 knowledge of which we are indebted to the investigations 

 of Selmi, Gautier, Nencki, and Brieger. The ptomains be- 

 long to the group of amins and ammonium-bases for 

 instance, cadaverin (pentamethylendiamin), putrescin (tetra- 

 methylendiamin), cholin, betain, neurin, and muscarin ; of a 

 portion of these substances only the chemic formula has 

 been determined, although their constitution is as yet un- 

 known for example, saprin, gadinin, etc. 



A knowledge of the metabolic products named is of the 

 highest diagnostic significance in bacteriologic investigation. 

 It is important to know whether a bacterium gives rise 

 to the formation of acid or alkali, whether it causes coagu- 

 lation of milk and liquefies gelatin by peptonization, whether 

 it generates phenol and indol, to what extent it reduces 

 nitrates, whether it forms gases, an-d which. All of these 

 peculiarities may be of determining significance for the iden- 

 tification of a given bacterium. 



Of considerable importance are the chemic activities dis- 

 played by bacteria in the domain of physiology &&& of pat/iol- 

 ogy. Bacteria participate in the normal course of the diges- 

 tive process in the huma.n intestine ; the interesting experi- 

 ment of Thierfelder and Nuttall, who, with complete exclu- 

 sion of all bacteria, fed with sterile nourishment a young 

 animal removed sterile by Cesarean section from the uterus 

 of a pregnant mother, demonstrates that this participation 



