58 BACTERIOLOGY. 



able nutrient material, at first, in spite of the 

 presence of oxygen, products due to splitting 

 are formed, and it is only subsequently that 

 oxidation of these products takes place. For 

 this reason, it is necessary, if one wishes to com- 

 pel aerobes to grow without oxygen, to work 

 with them in a young condition. Cholera cul- 

 tures are virulent when young, first becoming 

 impotent through access of air. For the same 

 reason our cultures of pathogenic bacteria upon 

 gelatin, agar, and potato, and in broth, are gen- 

 erally without power to produce disease, since, 

 in consequence of the restriction of metabolic 

 activity to the splitting of certain substances, 

 they have accustomed themselves so thor- 

 oughly to a metabolism based on oxidation, that 

 the poisons that w r ere formed in the first in- 

 stance through decomposition are rendered 

 harmless through the subsequent oxidation. 

 Ultimately, therefore, the formation of these 

 poisons comes to a standstill. 



Engelmann I actually observed that one spe- 

 cies of Spirillum had a distinct preference for 

 a certain tension of oxygen and always took up 

 its position between the edge and centre of the 

 drop of fluid in which it was suspended, at a 

 point dependent on this tension. If the ten- 

 sion of the oxygen was diminished by the 



i Arch. Neerland, XXVIII, p. 358. 



