26 BACTERIOLOGY. 



notably by the Bacterium urese. The change produced is represented 

 by the following formula : — 



COJ^^j + 2ffO = (NHO 2C0^ 



Clostridium butyricum converts the salts of lactic acid intO' 

 butyric acid, producing the butyric fermentation in solutions of 

 starch, dextrine, and sugar. These bacteria are agents in the 

 ripening of cheese, and the production of sauerkraut. Thus, in a 

 solution neutralised with calcium carbonate : — 



2[Ca(C'H=0-'')'] + H^'O = Ca(C^H'O-)'^ + CaCO» + 300' + H'. 



Tn the so-called viscous fermentation of wines, Streptococcus viscosus- 

 produces a gummy substance. According to Pasteur, the change 

 may be thus represented : — 



2.5(C"H'=0") + 25(H''0) = 12(C"'ff»0'°) + 24(C''H>*0'') + 

 12(00^) + 12(H20). 



And as another example, the Bacillus acidi lacticimay be mentioned,, 

 through the agency of which sugar of milk is converted into lactic 

 acid : — 



C'^H^O'^ = 4(C'H«0'). 



Saprogenic or putrefactive, bacteria play a most important part 

 in the economy of nature. They produce changes allied to fermenta- 

 tion in complex organic substances. Their action on proteids, 

 according to Hoppe-Seyler, may be compared to digestion ; bodies 

 like peptones are first produced, then leucin, tyrosin, and fatty 

 acids ; lastly indol, phenol, sulphuretted hydrogen, ammonia, carbonic 

 acid, and water. They abstract the elements they require, and the 

 remainder enter into new combinations. Associated with the forma - 

 tion of these substances are certain bodies which have a poisonous 

 effect when introduced into animals. These poisonous alkaloids, 

 ptomaines, produce a septic poisoning, which must be distinguished 

 from septic infection. The effects of septic poisoning depend on the 

 dose, whereas the effects of septic infection are, to a certain extent, 

 independent of the dose. A small quantity of a septic poison may 

 produce only transient effects, and a relatively, large quantity may 

 be necessary to produce vomiting, rigors, and death. Septic in- 

 fection, on the other hand, may result equally from a small dose, 

 because the poison introduced is a living organism which is capable 

 of propagation and multiphcation. Our knowledge of these 

 alkaloids is largely attributable to the researches of Selmi, Gautier, 

 and Brieger, and the result of their work will be referred to again. 



