448 Gary N. Calkins. 



like. The actual amount of water that was used for each isolated 

 individual was one-half a cubic centimeter. This was contained 

 in a small chamber consisting of a hollow-ground slide, two glass 

 supports about 3 mm. thick, and a thin glass cover. The Para- 

 incecium had ample room, therefore, for free movement, and an 

 actual depth of water of more than an eighth of an inch. Pres- 

 sure, therefore, was out of the question. In such a slide chamber 

 individuals were kept (/. e.^ extra individuals from the "stock") 

 for periods considerably longer than six weeks without change of 

 water, showing that the mere quantity was sufficient in order to 

 keep the animals alive. Foulness of the water, accumulation of 

 carbon dioxid, lack of oxygen, etc., were all guarded against 

 by the almost daily transfer of the culture individuals into fresh 

 hay infusion. The salt content of the water remained practically 

 constant, for fresh hay infusion was used each time with the same 

 amount of hay from the same source while the weekly analysis 

 of Croton water shows only minor fluctuations in the small 

 quantity of salts in solution. The gradual decrease in vitality 

 cannot be attributed to these causes, a similar phenomenon being 

 a matter of common observation and noticeable in any culture of 

 protozoa, no matter how large the vessel, nor what the species. 

 The light conditions were similar to those in any laboratory, the 

 culture vessels being kept before a window with north exposure. 



In regard to the possible objection that the Paramcecium ob- 

 tained only one kind of food, and therefore that the conditions 

 were abnormal in this respect, it may be stated that such a condi- 

 tion of treatment is a sine qua non of the experiments, and the only 

 possible means of controlling the results, and as I have demon- 

 strated, it is by a change of diet, including salt constituents, that 

 the periods of depression are overcome. This objection, there- 

 fore, begs the question of an object of the investigation. 



It seems quite unnecessary to repeat again that the only normal 

 life possible to Paramcecium caudatum is in the ponds where it is 

 subject to the changes in chemical composition of the water, to 

 the exigencies of drought, of heat, of freezing, and of rest by 

 encystment or lack of food. In the laboratory the protoplasmic 

 activities get no rest, but day after day they are maintained at the 



