DYNAMICS OF MORPHOGENESIS 203 



accumulation of lipoids in the nervous system, is very great, the 

 coefficient of distribution may be a very important factor in 

 determining the concentration of the narcotic in the nervous 

 system and so in determining its physiological effect. But it is 

 evident that in such cases the fundamental relation between the 

 physiological effect of the narcotic and the rate of reaction in the 

 organism or organ is simply masked by the incidental factor of 

 coefficient of distribution. 



2. Certain differences in the action of different reagents 



Notwithstanding the general similarity in the physiological 

 and morphological effect of the different substances used thus far, 

 certain more or less characteristic differences exist. 



In the first place, there is a marked difference in the relation 

 between mortality and morphological effect. In alcohol, ether, 

 chloretone a considerable proportion of the pieces die in any 

 concentration high enough to produce a marked morphological 

 effect. In KCN, on the other hand, it is possible to obtain ex- 

 treme morphological effects without losing a single piece in large 

 series of several hundred pieces. Such a difference as this must 

 have some very definite meaning. 



But certain other minor differences appear to be more or less 

 characteristic of the different substances. For example, KCN 

 inhibits or retards the formation of the optic pigment to a greater 

 extent than any other reagent used. In many cases eye-spots 

 consisting only of the unpigmented areas are formed (Child '12, 

 pp. 124-125). The outgrowth of the auricles is also greatly re- 

 tarded or completely inhibited in KCN, although'the characteristic 

 unpigmented sensory area develops in the same manner as when 

 the auricle grows into its normal form. In general the consist- 

 ency and color of the new tissue formed in KCN differs to some 

 extent from that of tissue which develops in other reagents. 



Ether apparently inhibits the development of new tissue at 

 the cut surface to a very great extent : in some cases a new head, 

 or at least a ganglionic mass may develop in ether with scarcely 

 a trace of outgrowth from the cut surface (Child '12, pp. 120- 



