DYNAMICS OF MORPHOGENESIS 197 



For those forms where disintegration follows soon after death, 

 the direct method is of much greater value than the indirect. 

 In the first place, it is more accurate and permits the determina- 

 tion of smaller differences in rate of reaction. With the direct 

 method the rate of reaction during the first few moments after 

 the worms are placed in the reagent, or at most an hour or two, is 

 the chief factor in determining the time of death. With the indi- 

 rect method the rate of reaction during days or weeks is a factor 

 in the results, but during this time the rate may change in conse- 

 quence of gradual starvation, or in pieces in consequence of regula- 

 tory processes, moreover, external conditions, e.g., temperature) 

 may also alter the rate and so influence the result. To take a 

 case in point, suppose we compare large relatively old worms with 

 very small young worms. By the direct method the young worms 

 show a much higher rate of reaction than the old, but by the 

 indirect method the factor of starvation may give the results a 

 wholly misleading character ; in other words, the very small worms 

 with a much higher jate of reaction may, in spite of this rate, die 

 of starvation before the large old animals, with much lower rate, 

 die from inability to become acclimated. Nevertheless, it is of 

 interest to note that except in certain extreme cases of this kind 

 the smaller, younger animals live longer, even though they have 

 less material available for nutrition. It is perhaps possible that 

 in alcohol, with which most of my work by the indirect method was 

 done, these younger worms with their higher rate of reaction are 

 able to make some use of the alcohol as a nutritive substance. 

 This complicating factor is of course absent when KCN is used. 



If a concentration of alcohol near the limit at which acclimati- 

 zation becomes impossible, is used, the temperature factor may 

 appear very clearly: after the animals have been in the solution 

 for some time and are less vigorous than normal, a rise in temper- 

 ature of a few degrees may change the action of the reagent from 

 what I have called the indirect to the direct and the animal dies. 



All of these and doubtless other factors also, interfere with the 

 accuracy of the indirect method, but in the direct method they 

 can be eliminated with little difficulty. It is always desirable 

 to check by the direct method results obtained by the indirect. 



