TOXIC ACTION OF KCN ON PARAMECIUM AND DIDINIUM. 22"] 



after the fatty acid treatment. In the case of normally fertilized 

 eggs where hypertonic sea water would not have the above 

 "curative" effect, but could be nothing but injurious, he found 

 that with an exposure of 40 minutes a maximum susceptibility 

 occurred just after fertilization and immediately before and 

 during each cytoplasmic division; while maximum resistance 

 is 35 to 45 minutes after fertilization and just after each division. 

 R. S. Lillie ('16) finds an osmotic swelling taking place in Arbacia 

 eggs when placed in dilute sea water. The rate of this swelling 

 depends upon the degree of dilution of the sea water and the 

 condition of the eggs. The fertilized eggs have a higher resistance 

 to the osmotic swelling, and consequent cytolysis than the un- 

 fertilized; but shortly before the appearance of the cleavage 

 furrow the resistance rapidly declines to a minimum at the time 

 of the appearance of the furrow. Immediately after the comple- 

 tion of the furrow the former resistance returns. A similar 

 change is found at the second and third cleavages, and probably 

 occurs at all cell divisions. 



In looking for a cause or causes of the variability in resistance 

 of Didinium and Paramecium to KCN we are reminded at once 

 of the fact that Lyon found the periods of susceptibility to KCN 

 of the sea urchin eggs to correspond to those for hydrogen 

 which might lead to the conclusion that oxidations are interfered 

 with. Warburg ('14) and Loeb and Wasteneys ('13) have found 

 that the oxygen consumption of the sea urchin egg is actually 

 decreased by the presence of KCN. Child ('15) finds that 

 stimulated flat worms are more susceptible to KCN than the 

 unstimulated, and also that the worms which he found to have 

 a low resistance to KCN had a high rate of CO 2 production as 

 determined by Tashiro's biometer. He concludes from this fact 

 that there is a relation between the resistance to KCN and "the 

 rate of metabolic reactions, or certain of them, probably the 

 oxidations." He also finds that there is a marked difference 

 between old and young Planaria, and between starved and fed 

 Planaria of the same age. The young worms and the starved 

 worms show a greater degree of susceptibility than the older 

 worms and the well fed worms, respectively. The results given 

 above for Paramecium and Didinium are the same as those found 



