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THE SENSE OF SMELL 167 



This explains the interesting observation of Beclard, that 

 persons who have lost the projecting portion of the nose by disease 

 or injury have no sense of smell. In such cases the air passes 

 directly through the choanae, without ascending to the olfactory 

 region. 



In order to determine the path by which the air -current 

 normally passes through the nasal cavities, Paulsen (1882) in 

 Exner's laboratory performed an interesting experiment on the 

 head of a human corpse. He sawed through the cranium in the 

 middle line to expose the nasal fossae, and then applied small 

 pieces of red litmus paper to different regions of the nasal mucous 

 membrane at short distances from each other; after this he 

 reunited the two halves of the skull. He then set up artificial 

 respiration through a bellows of approximately the same capacity 

 as the lungs, which he attached to the trachea, and passed air 

 containing ammonia vapour through the nostrils, when the litmus 

 paper turned blue in the parts of the mucous membrane over 

 which the ammonia passed. 



The results of these experiments were quite clear. The 

 reaction of the litmus paper showed that the inspiratory air- 

 current describes a curve in the nasal cavity, first passing upward, 

 and then turning towards the choanae. Moreover, the air which 

 penetrates through the anterior portion of the nostril rises higher 

 than that which enters by the posterior portion. 



On reversing the direction of the current, i.e. when the air 

 charged with vapour is driven from the choanae to the nostril, the 

 result was quite different ; the curve described by the current of 

 air follows a somewhat lower level than in the previous experi- 

 ment. Zwaardemaker, Eranke, and more recently Danziger and 

 Eethi, essentially confirmed the results of Paulsen, although they 

 varied his method in different ways. Zwaardemaker used the 

 plaster cast from one-half of the nasal cavity of a horse in which 

 the septum had been replaced by a glass plate. A glass tube was 

 inserted into the posterior part, and the soot of a petrol lamp 

 placed in front of it blown through by means of an aspirator. 

 This could be followed by the eye, and it was seen that the region 

 innervated by the olfactory nerve remained free from soot. 

 Franke sawed through a human skull in the middle line, stained 

 the whole of the mucous membrane black, replaced the nasal 

 septum with glass, and blew white tobacco smoke through the 

 nostrils by a bellows, which showed up well through the glass 

 partition on the black ground. This experiment, like the preced- 

 ing, showed that in ordinary quiet breathing the air inspired 

 through the nostrils did not reach the olfactory region, but 

 described a curve over the middle meatus, and middle and upper 

 part of the septum. 



The observations made by Kayser on the living subject also 



