4 W. J. ('JU)ZIEH 



• 



For -/"o HXO3 the penetration time found (Chroniodoris tissue) 

 was 3.5 minutes; for ^, 4.3 minutes; whereas Xeoturus, under 

 water, was found to react to I'o HNO3 (0.5 cc. of the solution 

 being applied with a pipette) in 1 .5 seconds when stimulated on 

 the dorsal surface of the head, 5 seconds on the lateral mid-body 

 surface, and 2 seconds on the tail; with w HNO3 the reaction 

 times for corresponding locations were 5, 10, and (3 seconds 

 respectively.-* Even here, though the pipette tip was held within 

 approximately a centimeter of the animal's surface, the concen- 

 tration of the solution in the pipette does not represent the con- 

 centration which actually reaches the stimulated surface, as 

 already noted by Parker ('12, p. 222). The conclusion must 

 therefore be, that acids do not penetrate the skin w^ith sufficient 

 rapidity to affect the cells of the germinative layer. TKis con- 

 clusion must also be extended to alkalies, since Harvey ('10) 

 and others have shown the high impermeabilit}- of cells to 

 strong hydroxides. 



IV. In the light of the evidence just discussed, it seems im- 

 probable that the high concentrations of irritants employed by 

 Parker and others in studying reactions attributed to the com- 

 mon chemical sense produce any violently disruptive effects 

 when applied to the skin of aquatic animals. Indeed, so far as 

 concerns the skin as a whole, they do not penetrate at all,^ 

 and the cells of the germinative layer cannot be held to be ex- 

 posed to their action. 



This conclusion was verified, in the case of the spinal frog, by 

 experiments of the following type: 



1. The reaction time for the withdrawal of the frog's foot 

 from w CUSO4, is about 7 seconds (at 24 ?9). After being 

 withdrawn from the solution, the feet continue for some time 

 to be spasmodically contracted. These subsequent contractions 

 are entirely inhibited the instant a foot, just retracted fromCuS04, 



'' The reaction times were measured at 20°, while the penetration of the acid 

 was studied at 27°; the speed of penetration decreases markedly with falling 

 temperature. 



5 The mode of action of the stimulating agent on the individual receptor is 

 entirely another question. 



