310 J. HOWARD MUELLER 



known to induce growth. One is struck by the lack of reference 

 to the identity of the components of meat extract or meat infusion 

 which seem to be so universally favorable. Purine bases are 

 mentioned, but apparently on insufficient experimental grounds. 

 In fact the only piece of work which the writer has found in 

 which an effort was made to determine this point was reported by 

 Armand-DeUlle (1913), who claims to have substituted arginine 

 for meat infusion in media used for the cultivation of the tubercle 

 bacillus. Other work (Long, 1919) indicates that this organism 

 is able to grow on a great variety of substances, and one is not 

 justified in appljdng the conclusions of Armand-DeUlle to other 

 types of bacteria without further experimental evidence. The 

 possibiUty of obtaining some light on the requirements of patho- 

 genic bacteria from this point of \'iew is, however, fairly promising, 

 and it is the purpose of the present paper to outUne the method 

 of approach and to cite a number of preliminary experiments 

 which serve to indicate the hues along which work may be done. 

 The results already obtained with two of the factors which 

 it has been possible to single out and follow up has been made the 

 subject of two preliminary reports (Mueller, 1920), and will 

 shortly appear in greater detail. 



A word regarding the purpose of such an investigation and the 

 results which can be expected from it may not be out of place. 

 The present empirical methods of media preparation are gen- 

 erally admitted to be uncertain from the standpoint of result, 

 and wasteful in materials used. It may be justly questioned, 

 however, whether a more thorough understanding of require- 

 ments will lead to a radical change in our methods of prepara- 

 tion of media. For example, even if certain amino acids and 

 organic bases should prove to be the only essential factors be- 

 side salts and perhaps carbohydrates, the difficulty and expense 

 of obtaining them in pure form might well prevent their ex- 

 tensive practical use, and it is quite possible that peptone and 

 meat will continue to be their most available source. It should, 

 however, be possible to understand the reasons for the uncer- 

 tainty of results and occasional failures now existing, and per- 

 haps to guard effectively against them, even though with ex- 

 perienced workers, they occur rather rarely. 



