J. (niOZIEK 



more iinjKM'vious hiyer of cells," the disintejj;ratioii of the sensi- 

 tive cells would cause exceedingly violent disturbances, pre- 

 sumably affecting tactile and pain terminals; and further, that 

 it has not been satisfactorily demonstrated that it is possible 

 (as claimed by Sheldon and by Cole) to effect a separation 

 of tactile and 'common chemical' irritability in fishes and 

 amphibians. 



This general argument is somewhat strengthened by the fact 

 (to which Coghill does not refer) that aquatic vertebrates pos- 

 sessing a soft slimy skin — cyclostomes, eels, catfish, Necturus — 

 are known to react to local irritation by chloroform and other 

 substances by the expulsion of mucus and even of entire gland 

 cells. The reaction time of this response is not known accu- 

 rately, though it is judged to be much greater than that, for 

 example, of the catfish as a whole when stimulated by hydro- 

 chloric acid applied to its trunk region; still, it is not incon- 

 ceivable that mechanical deformations brought about in this 

 way might provide stimuli for tactile nerve endings, provided 

 the mucus response were sufficiently sharp and prompt. 



II. The exact manner in which solutions are to produce the 

 hypothecated effects upon the cells of the germinative layer 

 is left entirely untouched by Coghill. The rapidity of the re- 

 sponses given by the catfish and Necturus immediately negatives 

 the idea that osmotic transfer of water is the agency of stimu- 

 lation. In the case of the spinal frog, as studied by Braeuning 

 ('04), Loeb ('05), and Cole ('10), though the reaction times are 

 rather long, there is abundant evidence that other than osmotic 

 factors are at work. The most important point which arises 

 for consideration is the extent to which chemical stimulants 

 actually penetrate the skin, i.e., the degree to which the cells of 

 the germinative layer are exposed to the action of the stimu- 

 lant. In addition to the rapidity of the reactions under discus- 

 sion, it is to be remembered that they are excited by acids, salts, 

 alcohols, and a variety of other-substances. 



That the skin of aquatic animals is not to any appreciable 

 degree damaged by the agents responsible for 'common-chemical- 

 sense' reactions, is clearly indicated by such facts as the following: 



