CULTURAL REQUIREMENTS OF BACTERL\ 323 



this may have been due to the loss of some essential factor in a 

 form which could not be recovered, as for example a tannin 

 precipitate or an extremely insoluble silver combination, as to 

 actual chemical decomposition of the substance. It is, in fact, 

 quite probable that there are many essential factors present, and 

 that progress can be made only as methods are developed which 

 will enable one to single these out for identification. Such a 

 method seems to have been found in the treatment of meat infu- 

 sion with charcoal. By this means, one or more factors are re- 

 moved from the infusion which may be again suppUed by the 

 addition of a small amount of peptone, or of a sulphuric acid 

 hydrolysate of casein. In following up this lead, a considerable 

 amount of work has been done, and a number of interesting 

 observations made which have alreadj^ been briefly reported 

 (Mueller, 1920) and which will be dealt with in the next paper 

 of this series. 



SUM*L4.RY 



The purpose of this paper has been merely to outUne the plan 

 of work and describe the method followed in our studies upon the 

 problem of the nutritional requirements of certain bacteria. 

 The procedures as outlined in the section on methods will be 

 used in such work unless modifications prove desirable. Suffi- 

 cient e\'idence has been obtained from the experiments here 

 reported to warrant belief that two classes of organic compounds 

 (in addition to carbohydrates), are required for the growth of 

 pneumococci and streptococci, the first suppUed bj' protein 

 degradation products, the second by extractives of meat. Both 

 occur together in ordinary meat infusion, but they may be separ- 

 ated more or less completely in several ways. The necessity 

 for a non-protein substance is shown most clearly by the failure 

 of a trypsin digest of purified casein to support growth, while 

 that of impure casein is satisfactory. The possibility of a sep- 

 aration of the two classes of compounds, as they occur together 

 in meat is evident from experiments of several tj'pes, particu- 

 larly by repeated extraction of meat, alcoholic precipitation of 



