712 TASTE AND SMELL. [CH. LIT. 



of the same side of the brain. This is the region of the brain experi- 

 mentally found to be associated with the sense of smell (see p. 679). 

 The olfactory bulb has a more complicated structure; above there 

 is first a continuation of the olfactory tract (white fibres enclosing 

 neuroglia) ; below this four layers are distinguishable ; they are 

 shown in the accompanying diagram from Ramon y CajaPs work, 

 the histological method used being Golgi's. 



535. Nervous mechanism of the olfactory apparatus. A, bipolar cells of the olfactory 

 apparatus (Max Schultze's olfactorial cells) ; B, olfactory glomeruli ; c, mitral cells ; 

 D, granule of white layer ; E, external root of the olfactory tract ; F, grey matter of 

 the sphenoidal region of the cortex ; a, small cell of the mitral layer ; J, basket of a 

 glomerulus ; c, spiny basket of a granule ; e, collateral of the axis-cylinder process of 

 a mitral cell ; /, collaterals terminating in the molecular layer of the frontal and 

 sphenoidal convolutions ; g, superficial triangular cells of the cortex ; h, supporting 

 epithelium cells of the olfactory mucous membrane. (Ramon y Cajal.) 



(1) A layer of white fibres containing numerous small cells, or 

 "granules " (D). 



(2) A layer of large nerve-cells called "mitral cells" (c), with 

 smaller cells (a) mixed with them. The axis-cylinder processes of 

 these cells pass -up into the layer above and eventually become fibres 

 of the olfactory tract E, which passes to the grey matter of the base 

 of the brain F. They give off numerous collaterals on the way (e, f). 



(3) The layer of olfactory f/lonieruli (B). Each glomerulus is a 

 basket-work of fibrils derived on the one hand from the terminal 

 arborisations of the mitral cells, and on the other from similar 

 arborisations of the non-medullated fibres which form the next layer. 



(4) The layer of olfactory nerve-fibres. These are non- 

 medullated ; they continue upwards the bipolar olfactory cells, 

 or as we have already termed them, the olfactorial cells of the 

 mucous membrane. 



In testing a patient's sense of smell, substances like musk or 

 assafcetida should be employed ; pungent substances like ammonia 



