BLOOD SERUM MEDIA 167 



various "extractives" which diffuse out with the salts 

 deprives the serum of any of its advantageous properties 

 remains to be ascertained. 



From the discussion of the physiological activities of bac- 

 teria in Chapters IX-XII it is apparent that a very great 

 variety of culture media other than those described is neces- 

 sary for the study of special types of bacteria, but such 

 media are beyond the scope of the present work. 



The ideal culture media are without a doubt the synthetic 

 media, that is, media of definite known chemical composition, 

 so that the various changes due to the growth of bacteria 

 can be accurately determined and thus a means of sharply 

 differentiating closely related organisms be secured. Such 

 media have been prepared and every bacteriologist believes 

 strongly in their future usefulness when media of wider 

 application shall have been devised. An example of this 

 type of culture media is Uschinsky's synthetic medium, of 

 which the following is one of the modifications: 



Distilled water . . 1000 parts 



Asparagin . . . . . . 4 " 



Ammonium lactate . 6 " 



Disodium phosphate . : 2 " 



Sodium chloride . . . . . 5 " 



A criticism of this medium is that the elements K, Ca, 

 Mg, Ee, Mn, and S which have been shown to be essential 

 are not present if chemically pure salts are used in the 

 preparation. 



