CULTURAL REQUIREMENTS OF BACTERIA 



317 



hours. In recording growth, such tubes are marked "A." This 

 autolysis is of course not a criterion of good growth, for in experi- 

 mental media, scanty growth is also followed by clearing up. 

 The streptococcus appears not to show this phenomenon. 



Preliminary experiments on infusion broth 



The growth of the test organisms on peptone-free infusion and 

 on peptone water alone was first investigated. 



I Meat infusion 25 cc. 

 Glucose-salt solution 25 cc. 

 Peptone' .5 gm. 



J . „ fMeat infusion 25 cc. 



\Glucose-salt solution 25 cc. 



I Peptone .5 gm. 

 Water 25 cc. 

 Glucose-salt solution 25 cc. 



It appears from this experiment that peptone-free infusion is 

 practically as satisfactory a medium for the growth of the pneu- 

 mococci and streptococci as the usual meat infusion broth con- 

 taining 1 per cent of peptone. On the other hand, with the 

 exception of the strain of Type I pneumococcus, peptone water 

 alone will not support growth. As a working hypothesis, it 

 has been assumed that these organisms have a nitrogen require- 

 ment supphed by peptones or amino acids, and also a need for 

 certain accessory substances supphed by meat infusion. There- 

 fore, on the basis of such a supposition, meat infusion seems to 

 contain not only the accessory substances, but also peptones, 

 amino acids or other sources of available nitrogen. The problem 



• Throughout the work, "Difco" Peptone has been used for the sake of uni- 

 formity. 



