392 C. M. CHILD. 



the axis or axes to cyanides and various other agents used in 

 concentrations sufficient to kill in the course of a few hours, 

 but not high enough to kill immediately and not low enough to 

 permit the organisms to become acclimated or acquire a tolerance 

 to them. The agents used in these studies on the sea urchin 

 were potassium cyanide, ammonium hydrate, ethyl alcohol and 

 hydrochloric acid in sea water. The various developmental 

 stages were placed in concentrations of these substances deter- 

 mined by preliminary experiment and the progress of death 

 along the axis was observed. 



In many of the lower animals the progress of swelling, cy tolysis, 

 separation and disintegration serves directly as an indication of 

 the progress of death. In the developmental stages of the sea 

 urchin changes of this sort occur as the cells die, but they differ 

 somewhat with different reagents and different stages of develop- 

 ment. In KCN the cells swell, become spherical, and separate 

 from each other as they die and the region concerned breaks down 

 into a shapeless mass of these spherical cells which soon dis- 

 integrate. If motor activity is still present in other parts the 

 dead cells may be progressively left behind as the living portion 

 moves about. This disintegration of the body is more marked 

 in the earlier stages of the blastula and gastrula than in later 

 stages where supporting tissues have differentiated, but even in 

 the later stages extensive disintegration can be brought about 

 by return to sea water after a sufficient length of time in KCN. 

 These death changes are somewhat accelerated and intensified 

 by the return to water and death is marked by very complete 

 disintegration. Thus when KCN is used, the progress of death 

 can either be followed directly under the microscope in the KCN 

 solution, at least in the blastula and gastrula stages, or lots may 

 be returned to water at stated intervals and the progress of 

 death determined by the comparison of dead and living portions 

 of the body in successive lots. Both methods have been used, 

 but the latter is more satisfactory in many cases, because after 

 return to water the dead portions disintegrate rapidly and com- 

 pletely while the parts which are still alive may recover and 

 resume motor activity where the stages in which movement 

 occurs are concerned. The progress of death can also be made 



