CULTURAL REQUIREMENTS OF BACTERIA 311 



Perhaps the most important results to which success in such 

 a piece of work might lead, are the applications of the findings 

 to problems of more general biological importance, particularly 

 to those of animal metaboHsm. For, whatever may prove to 

 be the nature of these substances which cause growth of bac- 

 teria, they are largely or entirely components of animal tissue, 

 and it is probable that they are either needed also bj' the animal 

 bodj^ and supplied by plant or other sources, or else are synthe- 

 sized by the animal itself to fill some metabolic requirement. 

 When it is possible to catalogue the substances required by 

 pathogenic bacteria for growth, it will probably be found that 

 most of them are either required by, or important in, animal 

 metaboUsm, and while many of them will surely be compounds 

 at present familiar to the physiological chemist, it is equally prob- 

 able that some will be new, or at least of hitherto unrecognized 

 importance. This point is sufficiently clear in the light of many 

 recent publications in connection with the relation of vitamines 

 to the growth of bacteria and of yeast. 



Probably of no less importance will be the results from the 

 standpoint of the classification of bacteria. Doryland (1920) 

 has discussed this question at some length, and it is quite possi- 

 ble that unexpected relationships or dissimilarities in bacterial 

 species may develop on the basis of food requirements. That 

 related species among pathogenic bacteria do have similar needs 

 cannot be questioned. The colon-typhoid group grow easily 

 on simple meat extract broth. The streptococci and pneumo- 

 cocci require the presence of an infusion of meat, the meningo- 

 cocci and gonococci usually grow poorly without the additional 

 presence of "hormones," blood serum, etc., while the influenza 

 bacillus needs a substance associated with hemoglobin. It is 

 quite possible that the more fastidious types of bacteria may 

 require some of the factors necessary for the more easily growing 

 forms, plus one or more additional substances. For example, 

 if growth of the typhoid bacillus depends on the presence of 

 three compounds in meat extract broth, A, B, and C, then the 

 pneumococcus will perhaps fail to grow unless A, B, and C are sup- 

 plied together with D and E, and so on to such organisms as the 



