I 



Nutrition of Bacteria. 199 



Although Bacillus influenzae will grow luxuriantly when trans- 

 planted from blood medium to plain broth containing yeast 

 extract, cultivation cannot be continued more than one or two 

 transfers in yeast broth alone. This suggested that possibly some 

 other substance may be carried over from the original blood culture 

 in an amount sufficient to supplement the yeast broth and that 

 growth fails in succeeding cultures because this substance is either 

 exhausted by growth or lost by dilution on subsequent transfers. 

 For purposes of discussion this substance may be referred to as 

 the X factor and the vitamine-like substance in the extracts as the 

 V factor. Neither of these two factors by itself can sustain growth 

 of Bacillus influenza. Evidently both are essential to growth 

 and both occur in blood which is always used in the cultivation 

 of Bacillus influenzae. As previously pointed out, the V factor it 

 destroyed by autoclaving. If, therefore, blood medium is auto- 

 claved, it should no longer be able to support growth of Bacillus 

 influenzas. This is actually the case. If, however, the X factor 

 has not been destroyed by heating then this same medium should 

 be reactivated by the addition of fresh yeast extract. This also 

 is the case. The growth accessory substance (the V factor) which 

 is destroyed by autoclaving blood, can be supplied from other 

 sources, such as yeast; and this substance is capable of reactivating 

 a medium in which, as a result of heating, the X factor alone re- 

 mains. Search is being made for the X substance in material 

 other than body tissue. That crystalline hemoglobin itself, 

 however, does not contain both of these essential substances, is 

 shown by the fact that pure crystalline hemoglobin when added 

 to broth fails to support growth of Bacillus influenzae unless yeast 

 or its equivalent in V substance is also present. This fact indi- 

 cates that crystalline hemoglobin contains some of the X factor. 

 Further studies are planned to determine the importance of this 

 principle in the cultivation of other species of bacteria. From 

 analogy with animal nutrition, it seems not unreasonable to suppose 

 that nutritional deficiency in the cultivation of bacteria may be 

 overcome by the addition to culture media of the appropriate 

 growth accessory substances. 



