INFECTION. 87 



appears to exert little or no influence upon the development of bac- 

 teria. 



Nitrogen. — The experiments of Pasteur have demonstrated that 

 an albuminoid nitrogenous substance is not necessary to the life of 

 bacteria, but that other nitrogenous substances, as ammonia, will 

 answer the same purposes. 



Pasteur's cultivating solution is as follows : 



Distilled water 100 parts. 



Sugar-candy 10 " 



Tartrate of ammonia 1 " 



Ashes of one gramme of yeast 0*075. 



Cohn's fluid is designed to counteract the development of mold 

 due to the cane-sugar in the above solution, and is as follows : 



Distilled water 100 parts. 



Tartrate of ammonia 1 " 



Ashes of yeast 1 " 



Mayer gives us another fluid which does away with the ashes of 

 yeast, viz. : 



Phosphate of potash 0-1 gramme. 



Sulphate of magnesia 0*1 " 



Tribasic phosphate of lime 0*1 " 



Distilled water 20 c. c. 



Carbon. — Aside from other sources, bacteria can obtain this im- 

 portant element to their life from organic acids. 



Oxygen. — Numerous controversies have taken place among sa- 

 vants as to the role this element plays in bacterial life. 



It seems, a priori, that, like other living things, oxygen must be 

 necessary to germ-life. Pasteur has demonstrated that it is not so, 

 however, with all forms of bacteria. In putrefying processes he has 

 demonstrated that, after certain species have developed B. termo, 

 which depend upon the presence of oxygen, and come to the surface, 

 forming a coating upon it, the fluid beneath is free from this gas, 

 and yet other forms of bacteria come to development in it. 



The first of these organisms — that is, those dependent on oxygen 

 for life — he has styled aerobic fungi, and the others anaerobic. 

 Other observers do not agree with this theory. Hoffmann, a very 

 able German savant, says : " These little beings can not live without 

 air — that is, without oxygen. If this gas is wanting, they cease to 

 move and to proliferate. If a drop of liquid full of bacteria is 



