Earlier experiments (Allee '12-'13) showed that certain conditions known to affect the rate of m'etabolism of animals regularly affected the rheotactic reaction of the isopod, Asellus communis, Say. Low oxygen, chloretone, potassium cyanide, lowered temperature, suddenly heightened temperature, increased carbon dioxide tension, and starvation, all of which depress the rate of metabolism of animals, also lower the positive rheotactic response of isopods. High oxygen, caffein, and a gradual increase in temperature have the opposite effect.
A desire to obtain more exact information regarding this correlation of metabolic rate and the rheotactic reaction of isopods led to an attempt to measure the rate of metabolism by means of the survival-time in potassium cyanide. This method was worked out by Professor Child ('13) for planarians, and is essentially as follows :
In a relatively strong solution of potassium cyanide (0.001 mol. or thereabouts) the animals having the highest rate of metabolism die first, or in other words, they have the shortest survival-time. Those having the lowest rate die last and hence have the highest rate of metabolism. Child called this the 'direct method' of 1 The experiments upon which this paper is based were performed in the Laboratory of Plant Physiology at the University of Illinois and in the Marine Biological Laboratory, Woods Hole, Mass. I am indebted to Dr. C. F. Hottes and Prof. F. R. Lillie for furnishing facilities for carrying on the experiments. I a m also indebted to Prof. C. M. Child and to Dr. Shiro Tashiro for many helpful suggestions, and to Marjorie Hill Allee for assistance with certain experiments and for aid in tabulating results.