136 VETERINARY PHYSIOLOGY 



Ferrier states that removal of the hippocampal convolu- 

 tion, including the lobus pyriformis, leads in monkeys to 

 loss of taste and smell, and that stimulation causes torsion 

 of the nostrils and lips, as if sensations of smell or taste 

 were being experienced. 



Other experimenters have observed interference with the 

 sense of smell in destructive lesions of the hippocampal lobe, 

 and one case at least has been described in which a tumour 

 of the right gyrus hippocampus was associated with sensa- 

 tions of smell. 



C. Physiology. — To act upon the olfactory mechanism 

 of terrestrial animals the substance must be volatile, and 

 must be suspended in the air. In this condition infinitesimal 

 quantities of such substances as musk are capable of 

 producing powerful sensations. The mucous membrane 

 must be moist, and this is secured by the activity of 

 Bowman's glands, situated in it. These are under the 

 control of the fifth cranial nerve, and section of this leads 

 indirectly to loss of the sense of smell through dryness of 

 the membrane. 



! 



II. FOR VIBRATION OF ETHER. 



Vision. 



A. General Considerations. 



While the addition to and withdrawal from the surface of 

 the body of the slower ethereal waves which are the basis of 

 heat act upon the special nerve terminations in the skin to 

 give rise to sensations of heat and cold, a certain range of 

 more rapid vibrations act specially upon the nerve-endings 

 in the eye. These produce molecular changes which in 

 turn affect the centres in the brain, and play a most 

 important part in the adjustment of movements for the 

 benefit of the body, and which give rise to changes in 

 consciousness which we call sight. The range of vibrations 

 which can act in this way is comparatively limited, the 

 slowest being about 435 billions per second, the most rapid 

 about 764 billions. Vibrations more rapid than this, while 



