Sheldon, Reactions to Chemical Stnniili. 297 



Tlionipsoii ill their rccout work. So far as the hnver vertehrates are 

 coneerued little work has heeii done on the siihjeet. Von Anrep 

 ('80) found that tactile reflexes disappeared before chemical, fol- 

 lowing the use of cocaine on the skin of the frog, while Parker 

 in his work on Ainphioxus and Auieiiirns showed that such a view 

 is fully supported ])}' the results obtained. It may, therefore, be 

 said that workers are agreed in assigning to the gustatory and 

 general cutaneous senses several sense qualities and that this work 

 falls in line in stating that, in the dogfish, the results secured by 

 the use of cocaine and by fatigue suggest that a separate mechanism 

 exists for the reactions to chemical as distinguished from general 

 tactile stimuli. 



From the evidence given we may say, with little hesitation, that 

 there exists a general chemical sense from the protozoa to man. 

 This general sense is the only chemical sense present in the lower 

 invertebrates; as we ascend in phylogeny, however, there are prob- 

 ably developed from it, as Ilerrick ('08) suggests, smell and taste. 

 The undifferentiated sense remains as the sensitiveness to chem- 

 ical stimuli exhibited by the nerves of general sensation in the 

 lower vertebrates and man. 



The association of chemical sensibility with the nerves of gen- 

 seral sensation need not in the least militate against the func- 

 tional analysis of the nervous system as elaborated by Herrick 

 ('O^a) and Johnston ('02, 'O(i), as it has never been assumed by 

 them that sensitiveness to chemical stimuli must be confined to 

 the nerves and organs of smell and taste. 



Summary, 



1. The smooth dogfish, Mustelus canis (Mitch.), is sensitive to 

 chemical stimuli over the entire body surface, mouth and nostrils, 

 responding by reactions which are characteristic for the dift'erent 

 regions stimulated. 



2. All parts of the body are very sensitive to acids and alkalis 

 in very dilute solution, less sensitive to salts and l)itter substances, 

 and do not react at all to sugars. 



3. CJertain ])arts of the general body surface are more sensitive 



