ACTION OF BACTERIAL FERMENTS. 29 



bacteria, sometimes wherever the soluble ferments reach 

 the organic substances. And in certain cases the ferments 

 diffused out into the surrounding fluid probably break down 

 the latter to some extent, and prepare it for a further, 

 probably intracellular, disintegration. Thus in certain putre- 

 factions of fibrin, if the process be allowed to go on naturally, 

 the fibrin dissolves and ultimately great gaseous evolution 

 of carbon dioxide and ammonia takes place, but if the 

 bacteria, shortly after the process has begun, are killed or 

 paralysed by chloroform, then only a peptonisation of the 

 fibrin occurs, without the further splitting up and gaseous 

 production being observed. That a purely intracellular 

 digestion may take place is illustrated by what has been 

 shown to occur in the case of the micrococcus ureae, which 

 from urea forms ammonium carbonate by adding water to 

 the urea molecule. Here, if after the action has com- 

 menced, the bacteria are filtered off, no further production 

 of ammonium carbonate takes place, which shows that no 

 ferment has been dissolved out into the urine. If now the 

 bodies of the bacteria be extracted with absolute alcohol or 

 ether, which of course destroy their vitality, a substance is 

 obtained of the nature of a ferment, which, when added to 

 sterile urine, rapidly causes the production of ammonium 

 carbonate. This substance has evidently been contained 

 within the bacterial cells. 



As has been said, some bacteria seem to be capable of building up out 

 of simple chemical compounds bodies which are more complex. This 

 function is best illustrated in a group of bacteria which probably play 

 a most important economic function in fertilising the soil by converting 

 ammonia compounds into nitrites and nitrates, and thus making the 

 nitrogen more available for plant nutrition. These so-called nitrifying 

 organisms have been investigated by Professor and Mrs. Frankland, 

 by Professor Warington, and by Winogradski. Their isolation pre- 

 sented great difficulties, none of the ordinary methods being available, 

 as the organisms sought were quickly overgrown by the ordinary 

 bacteria of the soil. Winogradski, however, succeeded in getting 

 fairly pure cultures by taking advantage of the fact that they were 

 capable of growing in the entire absence of organic matter, to exclude 

 which he took most elaborate precautions. The media used contained 

 potassium phosphate, sulphate of magnesium, sulphate of ammonium, 



