/'/: A'.)/ i:.\r. i TK )N 



103 



Very careful chemical investigations on pure cultures will be necessary 

 before the chaos of phenomena presented by the putrefactive bacteria can 

 be arranged in something like order. In view of the present state of our 

 knowledge of these organisms, it will be best perhaps to make the definition 

 of a putrefactive bacterium rather wide, and include all bacteria with 

 saprogenic properties, whether they possess other plcotrophic properties 

 (e.g. zymogenic) or not. It is certain that many bacteria, almost all the 

 cocci for instance, and many pigment bacteria, are destitute of saprogenic 

 power. Saprogenic bacteria arc able to break up albuminous bodies of 

 every kind and of every morphological character, whatever organs of the 

 body they be derived from. The influence of these saprogenic properties in 

 the production of disease will be considered later on. 



Just as the Bacterium tcnno was formerly regarded as the only cause 

 of putrefaction, so was the Micrococcns urcae discovered by Pasteur regarded 

 as the specific microbe of urinous fermentation. 



Healthy human urine, sterile and acid when passed, becomes sooner 

 or later alkaline. The urea has been converted by addition of water into 

 carbonate of ammonia : 



CO (NH 2 ) 2 + 2H 2 O = CO 3 (NH 4 ) 2 . 



A similar decomposition is undergone by the uric acid and by the 

 hippuric acid in the urine of herbivores. It is caused by a bacterial ferment 

 and, as with the putrefactive organisms, it was formerly thought that one 

 species alone was at work. This was the Micrococcns rireae of Pasteur, 

 a short, almost spherical, non-motile cell generally growing in pairs (Fig. 22) 

 or little chains (71 and 112). We know now, however, that many different 

 kinds of bacteria are able to cause the ammoniacal fermentation of urine. 

 No less than sixty species are said to occur in manure and sewage, among 

 others the B. vulgar is. On the other hand, B. subtilis, B. anthracis, B. typ/ii, 

 V. cliolerac, the pus cocci, and many saprogenic forms arc unable to split up 

 urea. Conversely, the urea bacteria are incapable of decomposing albu- 

 minous bodies, which is not surprising, seeing how different the two processes 

 are chemically. 



The resting cells of the urea bacteria are everywhere present in urine, 

 manure, earth, air, and dust. All urine that is left exposed to the air is 

 sooner or later attacked by them, and its nitrogenous constituents arc 

 converted into ammonium carbonate. In this way the path is prepared for 

 the nitrifying organisms, by which the nitrogen is made ready for renewed 

 circulation through the tissues of green plants. 



The amount of nitrogen treated in this way by bacteria is enormous. 

 The sewers of Leipzig discharge every day, in the form of urine, no less 

 than 8,400 Ib. of nitrogen. 



The two great processes, putrefaction and ammoniacal fermentation, are 

 going on in nature uninterruptedly. In the soil, in the mud of lakes and 



