156 C. M. CHILD 



time. This total may be made up of many individual reactions 

 of difTerent or of the same rate, or it may consist of a continuous 

 reaction with variable or uniform rate. But from the amount 

 of reaction occurring in a given time we may determine the aver- 

 age rate for that time. If the method under consideration is 

 correct, it enables us to determine whether the average rate dur- 

 ing a given time is greater or less in one case than in another. 

 'The rate of reaction' as the term is used here, is then analogous 

 to the term 'rate of flow' as applied to a current of fluid. It is 



simply Y" • -'^^d finally, the method in its present form is 



only comparative: it serves merely for the comparison of differ- 

 ent rates without giving any information as to what the rate is in 

 any case. 



2. The relation between death and disintegration in depressing 



agents 



The reagents most used thus far in work along these lines are 

 ethyl alcohol and KCN. Enough work has been 'done mth 

 ether and chloretone to demonstrate that they give results essen- 

 tially similar to those obtained with alcohol. 



The first point of importance is that when an individual or 

 piece of Planaria dies in a not too highly concentrated solution 

 of any of these reagents it undergoes disintegration within a 

 short time after death. The process of disintegration consists 

 first in the breaking open and disappearance of the body epithe- 

 lium and second of a gradual swelling and separation of the tissues 

 until finally nothing remains but minute particles suspended in 

 the fluid or lying on the bottom of the vessel. The swelling and 

 increase in translucency of the tissues apparently follows alinost 

 at once after the death of the part concerned and probably results, 

 at least in part, from the increase in permeability which occurs 

 at the time of death. After this stage the process does not con- 

 cern us so closely for it consists merely in the gradual separation 

 of the dead cells and supporting tissues. 



The length of time between apparent death and disintegration 

 and the rapidity of disintegration vary according to temperature, 



