24 GENERAL MORPHOLOGY AND BIOLOGY 



be retained in the cells where they are formed. In the latter case 

 the bacterial protoplasm often must be thoroughly disintegrated, 

 e.g., by grinding, before the ferment is liberated. Sometimes 

 the breaking down of the organic matter appears to take place 

 within, or in the immediate proximity of, the bacteria, some- 

 times wherever the soluble ferments reach the organic substances. 

 And in certain cases the ferments diffusing out into the surround- 

 ing medium probably break down the constituents of the latter 

 to some extent, and prepare them for a further, probably 

 intracellular, disintegration. Thus, in certain putrefactions 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 chloro- 

 form, then only a peptonisation of the fibrin occurs, without 

 the further splitting up and gaseous production. 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 

 commenced 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 

 ferment has evidently been contained within the bacterial cells. 

 According to some, the intracellular ferments alone have the 

 capacity of initiating profound changes in material absorbed, 

 while the easily diffusible agents have only a hydrolysing power. 

 In the investigation of the phenomena of the ferment action of 

 bacteria, it has been noted in certain cases that the ferments 

 formed depend on the food supply offered to the bacterium. 

 Thus in one case a bacterium growing in starch forms diastase, 

 but it does not so do when grown on sugar. 



The disintegration of organic material, which is so prominent an effect of 

 bacterial growth, must be a by-effect in the synthesis of the complex sub- 

 stances of which the bacteria themselves are built up. The most striking 

 example of such synthetic power is presented in the case of the bacteria 

 which in the soil make nitrogen more available for plant nutrition by con- 

 verting ammonia into nitrites and nitrates. • Winogradski, by using media 

 containing non-nitrogenous salts of magnesium, potassium, and ammonium, 

 and free of organic matter, has demonstrated the existence of forms which 

 convert, by oxidation, ammonia into nitrites, and of other forms which 



