RELATION TO ENVIRONMENT CLASSIFICATION 33 



Meat infusion, however, will not suffice for some of the more 

 strictly parasitic species, such as the meningococcus and gonococcus, 

 and for satisfactory growth of these organisms a highly complex 

 substance, such as whole blood or serum, is necessary. It is not cer- 

 tain at present whether the required material is the whole protein 

 or some simpler substance occurring in the animal body. For ex- 

 ample, the influenza bacillus has been known for a long time to 

 require red blood cells for its successful cultivation. It was formerly 

 believed that the hemaglobin was the essential factor required by 

 this organism, but recently it has been shown 16 that if media are 

 prepared by the addition of blood followed by heatirig to 70 to 75, 

 and filtering the coagulum, much better growth is obtained than on 

 ordinary blood agar. Since the proteins, including the hemaglobin, 

 have been removed by coagulation and filtration, probably some non- 

 protein component of the red cell is required by this organism. 



Lloyd 17 has suggested that these substances present in blood t ai\d 

 animal fluids resemble the vitamines which are now recognized as 

 playing such an important role in animal metabolism. She found that 

 they were often removed from solution by filtering through paper 

 or cotton, and on this observation are based the extremely useful 

 hormone or vitamine media of Huntoon. 18 Whether or not these 

 substances are identical with, or merely resemble, the vitamines of 

 animal foods remains to be established. It has been recently shown; 

 however, that ordinary yeast 19 and Sclerotinia cinerea the organ- 

 ism, 20 which causes brown rot disease in fruits, require water soluble 

 B. vitamine for their growth. 



PARASITISM AND SAPROPHYTISM 



When we speak of bacteria as parasites or as saprophytes, we 

 classify them, primarily, according to their relationship to the bodies 

 of higher animals. "Parasites" are those bacteria which are capable 

 of living and multiplying within the human or animal body, whereas 

 the term " saprophytes " refers to the multitude of microorganisms 



16 Fleming, Lancet, 1919, I, 138. 



17 Lloyd, J. Path, and Bact., 21, 1916, 113. 



18 Huntoon, J. Inf. Dis., 23, 1918, 169. 



19 Williams, J. Biol. Chem., 38, 1919, 465. 



20 Willaman, J. Am. Chem. Soc., 42, 1920, 549. 



