316 J. HOWARD MUELLER 



per cent 



NaCl 1.0 



MgSO, .04 



CaClj .02 



KKiVOi .2 



Glucose 0.2 



Phenol red 80 cc. of 0.02 per cent solution per liter 



If all the components except the potassium phosphate are dis- 

 solved, and the solution diluted almost to the final volumebefore 

 this substance is added, calcium phosphate is not precipitated, 

 although a good deal is probably lost in the precipitate which 

 usually forms on adjusting the reaction and boiUng. 



Sterilization of media 



Since it has been shown that ten minutes autocla\-ing at 10 

 pounds pressure is even less destructive to sugars then the Arnold 

 temperature for three quarters of an hour, this method has been 

 used in most of the work. Practically no change in pH occurs, 

 and contaminations are exceedingly rare. 



Recording of results 



T\Tien growth has continued for twenty-four hours, the degree 

 of turbidity is recorded by comparing the tube ■with a set of seven 

 tubes containing suspended BaS04 (Koser and Rettger, '19) 

 ranging from the faintest trace of a cloud to a suspension as hea\'y 

 as the best growth obtained with these organisms on good media. 

 Negative growth is shown by " O," and anj' degree of growth by a 

 ntimber corresponding to the series numberof the BaSOi standards. 

 This affords a means of correlating experiments done at different 

 times, although of course it is not quantitative. It usuallj- 

 happens, however, with the pneumococcus cultures, that after 

 optimum growth has been reached, autolysis follows very quickly. 

 Within a few hours, a tube which has shown growth equal to 

 standard tube nos. 4 and 5 will clear up and become simplj' 

 opalescent. With Tj-pe I this happens quite regularly in less 

 than forty-eight hours on good media, since maxunum growth 

 is reached by this strain in fifteen to eighteen hours. Tj-pes II 

 and IIA grow more slowly, but are often autolyzed in forty-eight 



