24 E. J. LUND 



The experiment was repeated with closely similar results. At 

 lower temperatures the animals are always unable to eat. As 

 the temperature is raised and the activity of the cell increases, 

 the rate of feeding increases, continuing to increase nearly up 

 to the point where the cell is injured or killed by the heat. At 

 temperatures between 20° and 25°C. (i.^., at about the optimum) 

 the increase in the rate of feeding can be determined only by 

 using a very large number of individuals, since the variations 

 obliterate the effects when a small number is used. 



All the experiments relating to other conditions were carried 

 on at temperatures ranging between 20° and 27°C. Where neces- 

 sary (as in prolonged experiments on digestion) the teniperature 

 was kept constant to within 1° to 1.5°C., throughout the course 

 of the experiment, by keeping the organisms in moist chambers 

 in a constant temperature oven. 



d. Effect of HCl and NaOH on the feeding reaction. 



Experiment V. The medium used in this experiment (table 8) was 

 conductivity water.'' Any water less carefully purified is worthless for 

 such experiments, as was shown by experiments carried out with tap 

 water. By comparing the results it was strikingly evident that the 

 acid and base had reacted with the salts and other impurities in the 

 tap water and hence their effect was removed in low concentrations. 

 The animals were washed once in conductivity water before putting 

 them into the solutions. Time of feeding, twenty minutes (table 8). 



It is seen from table 8 that the base NaOH was much more 

 toxic than the HCl, and that as the concentraton was increased 

 the number of grains eaten became less and less. The chemical 

 relations of the food and medium will be considered in more 

 detail, later on (p. 29). 



e. Effect of strong white light on the feeding reaction. Bursaria, 

 when kept in dishes with a rather clear medium, often collect 

 in the greatest number on the side of the dish away from fairly 

 strong white light. It therefore became of interest to test what 

 effect continuous light of a high intensity would have upon the 

 rate of feeding. 



^ Prepared and used in the Department of Physical Chemistry for conductivity 

 measurements. 



