iv THE SENSE OF SMELL 173 



he refers to the work of Nagel, and contends that the experiments 

 made by Aronsohn on fishes are not above criticism. Aronsohn 

 offered to fishes ants' eggs dipped in clove oil or tincture of 

 asafoetida, and saw that they retreated from the food, even if 

 still several millimetres away from it. From this he argued that 

 the olfactory organs were excited, but Veress thought it equally 

 probable that the retreat was due to excitation of the tactile 

 organs. 



Notwithstanding these elaborate researches, we are hardly 

 justified in asserting that all classes of fishes are entirely unpro- 

 vided with the sense of smell, especially as the olfactory organs 

 are so highly developed. If it were so we should have to assume 

 that the olfactory cells of fishes have functions other than those 

 in air-breathing animals. 



Further, it is evident, as pointed out by Johannes Miiller, that 

 the essential part of an olfactory sensation lies not in the gaseous 

 nature of the odorous substance, but in the specific sensibility of 

 the olfactory organs, and in their differentiation from all other 

 sense-organs. 



On the other hand, there are direct observations, the earliest 

 of which date back to Aristotle, that tend to show that fishes 

 possess a sense of smell which is specifically distinct from all other 

 sensations. Milne Edwards points out that sharks often come 

 from afar to devour the carcases thrown into the sea, and that 

 other fishes of the same class show distaste for food that gives off 

 odours. Other authors, on the contrary, including Nagel, agree 

 with Veress in denying that fishes and aquatic amphibia have any 

 sense of smell comparable with that of terrestrial animals. 



The question seems to us to be decided by the experiments of 

 v. Uexkiill on Selachians (1894). He took certain specimens of 

 Scyllium that had been deprived of food for some time, and 

 extirpated the olfactory mucous membrane of the nasal fossae in 

 some, leaving it intact in others. He found a difference in the 

 behaviour of those which had and had not been operated on. The 

 latter, shortly after food had been placed in their tank, either 

 loose or in a bag, became very restless and began to swim in 

 search of it. According to v. Uexkiill washing the hands in the 

 tank after touching sardines was enough to throw the intact fishes 

 into a state of excitement. Those operated on, on the contrary, 

 seemed quite unaware of the presence of food, even when it was 

 placed close to them. 



These experiments seem to establish the existence of a sense of 

 smell at least in Selachians. Other experiments by v. Uexkiill 

 show it to be quite distinct from the sense of taste, as he found 

 that normal dogfish will take a sardine covered with quinine 

 sulphate into their mouths, but immediately reject it. Con- 

 sequently, it is not taste but smell which guides them in seeking 



