NITRIFYING BACTERIA. 431 



Winogradsky is a short, oval, and frequently almost 

 spherical cell. It divides as usual for bacteria, but 

 there is little tendency for the daughter-cells to adhere 

 together or to form chains. In cultures they are com- 

 monly massed together, by a gelatinous material, in the 

 form of zoogloea. They do not form spores, and are 

 probably not motile, though Winogradsky believes he 

 has occasionally detected them in active motion. As 

 has been stated, they do not grow upon the ordinary 

 nutrient media, and cannot, therefore, be isolated by the 

 means commonly employedin separating different spe- 

 cies of bacteria. The most astonishing property of this 

 organism is its ability to grow and perform its specific 

 fermentative function in solutions absolutely devoid of 

 organic matter. It is believed to be able to obtain its 

 necessary carbon from carbonic acid. For its isolation 

 and cultivation Winogradsky recommends the following 

 solution: 



Ammonium sulphate 1 gramme 



Potassium phosphate . . . 1 " 



Pure water .... ... 1000 c.c. 



To each flask containing 100 c.c. of this fluid is added 

 from 0.5 to 1.0 gramme of basic magnesium carbonate 

 suspended in a little distilled water and sterilized by 

 boiling. One of the flasks is then to be inoculated with 

 a minute portion of the soil under investigation, and 

 after four to five days a small portion is to be with- 

 drawn, by means of a capillary pipette, from over the 

 surface of the layer of magnesium carbonate and trans- 

 ferred to a second flask, and similarly after four or five 

 days from this to a third flask, and so on. As this 

 medium does not offer conditions favorable to the 

 growth of bacteria requiring organic matter for their 



