i 9 o8] HASSELBRINC— ASSIMILATION OF PENICILLIUM 187 



TABLE XV 

 In this series the amount of CH 3 COOK was 0.988™ per flask, but the magnesium 



content was varied. 



The potassium acetate cultures show a remarkable uniformity of 

 yield, which is independent of the concentration of the acetate, except 

 in very dilute solutions and probably also in very concentrated solu- 

 tions. The lowest concentration in tables IX and X is too dilute to 

 allow the full development of the fungus under those conditions, but all 

 the other concentrations give the same yield. 



With the increase of magnesium in the cultures, the yield is increased 

 but still remains uniform (table XV, col. I). A higher concentration 

 of MgS0 4 becomes poisonous. 



In the growth of all the potassium acetate cultures the medium 

 becomes alkaline, showing that only the CH 3 COO- radicle is taken 

 up by the fungus. The excess of KOH (or KHC0 3 ) results in the 

 precipitation of NH 4 MgP0 4 , thus keeping the culture neutral or only 

 slightly alkaline for a time. When all the Mg is precipitated, the 

 increased alkalinity prevents further growth. The addition of more 

 Mg delays this period, and hence gives a greater yield. The yield is 

 practically quantitative for a certain amount of Mg, and is independ- 

 ent of the amount of CH 3 COOK. 



The potassium acetate cultures brought out the striking difference 

 in power of resistance to deleterious substances possessed by different 

 spores from the same culture. This was also observed in other cases 

 where deleterious concentrations of substances were used, but it was 

 nowhere as evident as in the potassium acetate cultures. By the 

 method of inoculation, it is likely that more than a thousand spores 

 were sown in each flask. In the favorable media a large percentage 



