312 J. HOWARD MUELLER 



gonococcus and others. Such a conception will at least serve 

 as a working hypothesis upon which to begin investigation. 



The choice of organisms with which to work must be governed 

 by several considerations. In the first place, since several fac- 

 tors are probably involved in the growth of all parasitic bacteria, 

 it would be well to select a species having a somewhat limited 

 number of requirements. In this way one might hope to single 

 out one or two factors at a time for identification and, using 

 these as a basis, proceed to the study of others. On the other 

 hand, bacteria with too simple requirements should be avoided, 

 because of the probability that such organisms possess the power 

 of using a variety of difi'erent materials ha\-ing no immediate 

 relationship to the components of meat extract and peptone. 

 The colon bacillus, for example, can grow on Uschinsky's or 

 other simple media, about as well as on ordinary extract broth, 

 and for that reason would not be suitable for the purpose at 

 hand. A further point to be considered is that since the work 

 will probably extend over a long period of time, the type of or- 

 ganism selected must be such that its cultural requirements wiU 

 not change materially during preservation on culture media. 



For these reasons, the pneumococcus-streptococcus group was 

 selected as being probably the most satisfactory. These organ- 

 isms grow well on meat infusion broth, but poorly or not at all 

 on extract broth. While blood or serum improves the growth, 

 neither is essential. In addition, these organisms can be pre- 

 served almost indefinitely and kept at what should be quite 

 uniform food requirements. The method by which this is at- 

 tempted will be described fully below. 



The original plan of the work was to start with meat infu- 

 sion-peptone broth, to eliminate such factors in its composition 

 as could be managed experimentally, and to substitute known 

 compounds, such as amino-acids, purine bases, etc., or failing 

 in this, to determine, if possible, the chemical nature of the 

 material removed from the media. As will appear, the work 

 has been little more than begun, since the difficulties in substi- 

 tuting known compounds for the meat infusion have proved 

 unexpectedly great. 



