PRODUCTS OF BACTERIA. 33 



best in media of a neutral or very slightly alkaline 

 reaction, any excessive production of alkalinity or 

 Etcidity, as a product of growth, arrests development, 

 and no evidence of life or further multiplication can be 

 detected until this deviation from the neutral reaction 

 has been corrected. 



Most favorable for the development of bacteria are 

 neutral or very slightly alkaline solutions of albumin in 

 one form or another. 



Of considerable importance and interest in the study 

 of the nutritive changes of bacteria is the difference in 

 their relation to oxygen. With certain forms oxygen 

 is essential for the proper performance of their func- 

 tions, while with another group no evidence of life can 

 be detected under the access of oxygen, and in a third 

 group oxygen appears to play but an unimportant part, 

 for development occurs as well with as without it. It 

 was Pasteur M'ho first demonstrated the existence of 

 species in the bacteria family which not only grow and 

 multiply and perform definite physiological functions 

 without the aid of oxygen, but to the existence of 

 which oxygen is positively harmful. To these he gave 

 the name anaerobic bacteria, in contradistinction to 

 another group for the proper performance of whose 

 functions oxygen is essential; these he called aerobic 

 bacteria. In addition to these, there is a third group 

 for the maintenance of whose existence the absence or 

 presence of oxygen is apparently of no moment — their 

 development progresses as well with as without it ; these 

 represent the class known as facultative in their re- 

 lation to this gas. It is in this third group, the faculta- 

 tive, that the majority of bacteria belong. Though the 

 multiplication of the facultative varieties is not inter- 



