PHYSIOLOGY OF OLFACTION 45 



The course that the current of air takes through the 

 nasal chamber during quiet respiration has been studied in 

 several ways. Paulsen in 1882 published the results of ex- 

 periments on the human cadaver. He opened the nasal 

 cavity by sawing through the head of a cadaver close to 

 the median plane. Pieces of red litmus-paper were then 

 placed on different parts of the nasal surface and the two 

 halves of the head were brought together again. By 

 means of a bellows attached to the trachea of the cadaver, 

 the current of air that in life passes through the nasal 

 chambers was imitated. This artificial current was 

 charged with ammonia and thus a means was given of in- 

 dicating the spread of the current by the location of the 

 pieces of litmus-paper that changed from red to blue. As 

 a result of this test it was found that the inspired air took 

 a curved course from the naris to the choana. (Fig. 12). 

 The highest part of this curve was near the middle of the 

 nasal cavity, but this never reached a point as high 

 as the olfactory cleft. When the current was reversed 

 by causing it to enter at the choana and emerge at 

 the external naris, as in expiration, the direction of the 

 current was found to be much the same as in inspiration 

 except that a somewhat lower course was followed. Thus 

 in both inspiration and expiration the current of air is 

 limited to what is more generally regarded as the respira- 

 tory region of the nasal cavity, the olfactory region being 

 essentially undisturbed. 



Paulsen 's results were confirmed in all essential par- 

 ticulars by a number of later investigators including 

 Franke, Zwaardemaker, Danziger, and Rethi, who worked 

 on dead animals and human cadavers by methods not un- 

 like those used by Paulsen. Franke (1893) sawed open 



