174 PHYSIOLOGY 



CHAP. 



their food ; and they reject the unappetising morsel, not by smell 

 but by taste. 



Accordingly, even if Aronsohn's experiments on man were 

 carried out by an imperfect method, the conclusion he arrived at, 

 that the olfactory sense can be excited by odorous substances 

 dissolved in fluid, agrees well with what is known for fishes. 



Very few researches have been made on the olfactory organ 

 with inadequate stimuli. Among these the electrical current 

 alone has given some positive, even if doubtful, results. Volta 

 failed to observe any effect of an olfactory character; Hitter 

 obtained a special sensation similar to that aroused on looking at 

 the sun or sniffing up tobacco (excitation of tactile and pain 

 sense). He subsequently noted near the kathode the sensation 

 felt before sneezing, and occasionally a trace of ammoniacal 

 odour : at the anode, on the contrary, there was sometimes a 

 sensation of acid which may have been due to spread of current 

 to the taste-buds. More interesting results were obtained by 

 Althaus from a patient affected with bilateral paralysis of the 

 trigeminal nerve. On applying strong galvanic currents to the 

 Schneiderian membrane he obtained a smell of phosphorus. 



Aronsohn made a number of investigations by his method, 

 passing a current through the nasal fossae filled with an isotonic 

 solution of sodium chloride at 38. Different olfactory sensations 

 were aroused according as the anode or the kathode was applied. 

 The kathodic smell occurred during the closure of the circuit, the 

 anodic at the opening. The kathodic smell was regularly stronger 

 than the anodic. The quality of the two sensations, which 

 approximate to the gustatory impressions, was indescribable. 

 When an odoriferous substance in solution was employed, its 

 characteristic smell was altered by the electrical current. 



According to Valentin it is possible by mechanical stimulation 

 of the nostrils to produce unpleasant olfactory sensations which 

 last for some time. But other observers failed to obtain any 

 results. 



Thermal stimuli arouse no olfactory sensations, even when the 

 nasal fossae are filled with fluid at or at 50 C. 



IV. At present we know little of the chemical and physical 

 properties which a substance must have in order to be an adequate 

 stimulus of the olfactory end-organs. We are wholly ignorant of 

 the correlation between the physico-chemical constitution of a 

 body and the quality and intensity of the odours it is capable of 

 arousing. Some substances that differ greatly in chemical con- 

 stitution have much the same odour ; on the other hand, some 

 substances that are chemically allied have a very different smell. 



Haycraft (1888), Passy (1892), and Zwaardemaker (1895) 

 brought out some interesting facts in relation to this intricate 

 subject. In the periodic system of Mendeleeff and Lothar Meyer 



