CONTRIBUTIONS FROM THE ZOQLOGICAL I.ABOR\TORr OF THE MOSEUM OF CO.\rPARATIVE ZOOLOGT AT 

 HARVARD COLLEGE. NO. 2fi8. 



REGARDING THE EXISTENCE OF THE 'COMMON 

 CHEMICAL SENSE' IN VERTEBRATES' 



W. J. CKOZIKR 



I. In a recent paper by Coghill ('14) exception is taken to 

 the view held by Plerrick f'OS), Sheldon ('09), Cole ('10), and 

 Parker ('12), that there is in vertebrates a set of receptors (free 

 nerve terminations) which are responsible for reactions to rather 

 high concentrations of chemicals when applied to moist periph- 

 eral surfaces. The theoretical significance attached to this 

 'common chemical sense' (Parker, '12) makes it appropriate to 

 bring forward certain facts which may to some extent serve to 

 clear up the situation. 



The evidence adduced by ( "ojihill is tliis: that in Aiiil)lystoiua 

 larvae, before the estalilishment of the definitive nervous system, 

 tactile and chemical irritability appear concomitantly and, so 

 far as studied, remain completely parallel in development; and 

 that if larvae be placed in irritating solutions of hydrochloric 

 acid (as dilute as lo.wo)- ^^^^ epithelial cells become visibly 

 disrupted, the reaction of the larvae being correlated with the 

 disintegration of the skin and a grndual disappearance of reaction 

 to tactile stimuli. 



Plis conclusion, that tliere is not present in the skin any normal 

 irritability to acid, is probably correct for the larvae experi- 

 mented upon; but it by no means follows that the same con- 

 ditions obtain in the adult. Coghill argues, however, that the 

 permanently embryonic cells of the germinative layer in the 

 skin of amjaliibians and fishes when exposed to the high con- 

 centrations of acid (40) used by Parker and Sheldon act as do 

 the superficial ciliated cells of the Amblystoma larval skin. 

 Because they are bound down by a "thick, less sensitive, and 



^ Contributions from the Hernuida Biological Station for Kesearrh. Xo. 40. 



1 



THK JOl'RNAt. OK COMPARATIVE NEUROLOGY, \ OI.. 26, SO. 1 

 FEBntARY, 1916 



