DYNAMICS OF MORPHOGENESIS 199 



one supply of solution and obser\^ations extend over only a few 

 hours. 



But although the indirect method is much less valuable than 

 the direct for the comparison of rates of reaction alone it is of 

 great value in the analysis of morphogenesis for it enables us to 

 determine with some degree of certainty the relative rates of 

 reaction connected with different morphogenetic processes and to 

 inhibit the processes with lower rate (Child '12). Moreover, 

 I believe it will prove of value as a method for the experimental 

 study of acclimatization. Certain points of considerable interest 

 have already appeared in the course of my work with this method, 

 although I was chiefly concerned with other problems. For 

 example, the fact that old animals always die at a larger size than 

 young ones in certain low concentrations of alcohol must have 

 a very definite physiological significance. Under these conditions 

 the old animal is not able to use as large a proportion of its own 

 substance for nutrition as is the young animal. Possible inter- 

 pretations of this fact will be considered elsewhere. 



As regards the relative value of different reagents, there can 

 be, I believe, but one conclusion, viz., that the cyanides are far 

 more valuable than any of the others. The very low concentra- 

 tions which are used, as well as the constitution of the cyanides 

 practically eliminate various factors which may complicate the 

 results obtained with the narcotics in the stricter sense and leave 

 only the chemical factor. The results obtained with the cyanides 

 must, I think, be taken as the basis of the method and other 

 results must be checked by them. 



With pure reagents, water of constant constitution, constant 

 temperature, care in making solutions and the proper care of 

 stocks and selection of animals the direct resistance method is a 

 method of great delicacy and the complicating factors which 

 influence the results by the indirect method can be practically 

 eliminated in the direct method. The method is undoubtedly 

 capable of much further development as an exact method than I 

 have yet attempted. By standardizing the conditions of the 

 experiment and adopting a certain unit as a basis of measurement 

 we may obtain definite dynamic expressions for different ages. 



