THE NITRIFYING BACTERIA. 373 



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 zooglcea. 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 employed in separating different 

 species of bacteria. The most astonishing property of 

 this organism is its ability to grow and perform its 

 specific fermentive 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 sulpbate ... .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 car- 

 bonate suspended in a little distilled water and steril- 

 ized by boiling. One of the flasks is then to be inocu- 

 lated with a minute portion of the soil under investiga- 

 tion, and after four to five days a small portion is to be 

 withdrawn by means of a capillary pipette from over 

 the surface of the layer of magnesium carbonate and 

 transferred 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 develop- 

 ment, those that were originally introduced with the 

 soil quickly disappear, and ultimately only the nitrify- 



17 



