NEUEO-MUSCULAE MECHANISM 113 



pathic sense, while the peripheral nerves are the units for 

 epicritic sense (fig. 50). 



In the spinal cord there is no indication of separate channels 

 for these two kinds of nerves, but the sensory impulses get 

 shunted into special tracts for heat, cold, touch, etc. (see p. 206). 



He also considers visceral sensations. He finds that, when 

 water is applied to the inside of the colon, differences of 

 temperature between 20 and 40 C. are not appreciated, but 

 ice-cold water is felt as cold and water at 50 C. as hot. The 

 sensation is not localised. He argues that the viscera have 

 protopathic but not epicritic sensibility, but he points out that 

 most of the visceral sensations are due to a sense akin to 

 the muscle sense. 



He concludes that the body within and without is supplied 

 with protopathic fibres and with fibres associated with sensa- 

 tion of movement and of pressure, but that to the skin alone 

 epicritic fibres pass (fig. 50). 



How far epicritic sensibility exists in the lower animals it is 

 not easy to determine. Possibly it has been evolved in the 

 primates in connection with the important part played by the 

 tactile sense of the hand in directing the movements of the 

 animal. 



(c) FOR CHEMICAL STIMULI 

 Sense of Taste 



1. Receptors. These receptors are developed in the mouth 

 with the object of determining the utilization or rejection 

 of material taken into the mouth according as it is beneficial 

 or nocuous. 



The most important receptors consist of groups of spindle- 

 shaped cells with which the dendritic termination of the nerves 

 from the mouth are connected, each group of cells being 

 surrounded by a series of flat epithelial cells like the staves 

 of a barrel to form a taste bulb. These taste bulbs are most 

 abundant at the back of the tongue, on the sides of the large 

 circumvallate papillae which form the prominent V-shaped 

 line on the posterior part of the dorsum. 



2. Connections with the Central Nervous System. - - The 

 posterior third of the tongue is supplied by the glosso- 



8 



