Studies on the Life History of Protozoa. 435 



positive to the negative pole. At the end of the treatments the 

 four individuals appeared normal. On the following day one had 

 died, another on the ensuing day, and the last two on the fourth 

 day. Another time the same experiment was tried but with only 

 one minute of exposure. The result was the same, death without 

 division. The death of these organisms at this time cannot neces- 

 sarily be ascribed to the treatment, for a glance at the diagram 

 shows that the entire race was dying and that divisions were infre- 

 quent in all cases. 



4. Nitro-Glycerine. 



At the suggestion of Professor Wilson, and as a last resort, I 

 tried two experiments when the race appeared to be dying out in 

 December. Nitro-glycerine in very weak solution (unfortunately 

 I have no record of the strength used) was put into the hay 

 infusion. It made no appreciable difference in the final result 

 and the organisms did not divide. 



Professor Wilson's other suggestion seemed more hopeful, on 

 the a priori ground that renewal of vitality is effected by the union 

 of two individuals. A culture of Paramcecium fresh from 

 pond water was made, and hundreds of individuals were allowed 

 to dry in a small drop of water in a watch crystal. When dried 

 the remains were scraped together and pulverized, the powder 

 thus formed being added to the hay infusion in which the weak- 

 ened Paramcecium were kept. Although this extremely ingenious 

 suggestion was worthy of a fruitful result, the outcome of the 

 experiments was the same as with all the rest, and not a single 

 individual lived after the 19th of December, one week after six- 

 day treatment with the dried Paramcecium. 



There remain many experiments that might have been tried, 

 and that might possibly have accomplished the same results that 

 were obtained in the earlier periods of depression when the race 

 was successfully reinvigorated by artificial means, and even the 

 experiments that were tried might have been successful if different 

 strengths, or times of action, had been used. Many suggestions 

 were made by my colleagues and other friends, especially in 

 regard to the trial of some chemical compound. I am pleased to 



