180 CONTRIBUTIONS TO OUtt KNOWLEDGE OF SOIL-FERTIMTY, XVI. 



The greater growth of amoebie and the smaller probability of 

 the production of a toxic effect in aerated cultures raised the 

 idea that, like yeast-cells, the reproductive may be inversely 

 proportional to the physiological activity. So another experi- 

 ment was started, and, as a variation, a flask was included 

 which was infected with a culture of bacteria only, derived from 

 a protozoon-free droplet of a starter. The extracts were tested 

 on the sixth day. 



Experiment xxiv. 



The numbers bear out the contention that, if toxicity is to be 

 obtained, it will not be as the result of aeration. The reaction 

 went on as in the previous case, aeration producing acidity, and 

 no aeration, alkalinity in hay-infusion. The examination of the 

 culture-fiuids showed that the am eel Ke had begun to encyst in the 

 aerated, and that 1,000 mobile forms per c.c. were in the other. 



A further test was made upon the same lines; as a variation, 

 a deep layer of fluid was used without aeration in order to accent- 

 uate the conditions. The method at this time had been to use 

 700 c.c. of fluid contained in a bottle of about 1,200 c.c. capacit}', 

 and, in this, the fluid had a depth of 9 cm. In the deep test, 

 1,700 c.c. were used, and in an ordinary Winchester this had a 

 depth of 16 cm. In the latter, the amoebae grew slowly, the first 

 indication being obtained on the thirteenth day, when 330 per 

 c.c. were noted. On the seventeenth, they had risen to 1,000. 

 The aerated test showed 5,300 on the fourth, and, without 

 aeration, the first evidence, 330 per c.c, was obtained on the 

 eleventh day. 



