Olfactory Apparatus in Dog, Cat and Man 21 



bearing cells serve both to collect the molecules of odorous substance and 

 to serve directly in their perception. 



In 1862 he still had never seen the olfactory fibers connected with the 

 bipolar cells, but believed there was no ground to doubt this, and says: 

 "The future will prove this view through observation." 



Exner, 1872, alone disagreed. In his work on amphibia, birds and 

 mammals, he could find all intermediate stages between epithelial and 

 olfactory cells; the epithelial cells had all the characters attributed to 

 olfactory cells. He believed that the olfactory nerve fibers reached the 

 superficial connective tissue and terminated in a special greatly reticu- 

 lated layer,' the subepithelial network. From this network pass two 

 kinds of fibers, one of epithelial cells, one of olfactory cells. This net- 

 work forms, with the two kinds of cells, the terminal apparatus of the 

 olfactory nerve. Exner says : "It would be difficult to say whether all 

 parts of this apparatus serve in the same degree in the olfactory per- 

 ception." 



Cisoff, 1874- By use of isolation methods, Cisoff claims to have 

 seen the nerve cell with a long central varicose process, and also to have 

 seen the connection of these cells with nerve bundles. His work, how- 

 ever, seems not to be credited. 



von Brunn, 1875, worked on cat, dog, rabbit and sheep. He found 

 the epithelial cells and the olfactory cells. The olfactory cells were 

 pear-shaped with a round nucleus. Beneath the epithelium the central 

 process joined with other processes to form a network in which stellate 

 cells were found. The olfactory nerves were broken up in the same 

 manner in the upper part of the mucous membrane. He did not see 

 the direct connection of these fibers with the central processes of the 

 olfactory cells, and says, "I can only declare such a connection as pos- 

 sible." Both these and the retinal cells are, according to von Brunn, 

 bipolar sense cells with similar function. For mammals, he describes 

 a membrana limitans olfactoria, which covers the epithelial cells as a 

 whole. The peripheral processes of the olfactory cells project through 

 pore-like openings in the membrane. 



In 1880 von Brunn modifies his views concerning this membrana 

 limitans, and thinks it lies underneath the "rudimentary cilia" of the 

 epithelial cells. 



Ehrlich, 1886, by methylene blue established with certainty the direct 

 connection of the olfactory fibers and the bipolar cells of the mucosa. 

 This stain is very transitory and lasts only a short time, so the work 

 was not credited until confirmed by the Golgi method. 



