570 A MANUAL OF VETERINARY PHYSIOLOGY 



fact, distinct fibres exist for all the cutaneous senses ; those con- 

 veying pain do not transmit cold, and those transmitting cold 

 do not convey heat. It is remarkable that touch, heat, cold, 

 and pain senses are distributed over the surface of the skin in 

 spots or dots. There are spots which are responsive to pressure, 

 others to warmth, others, again, to coldness, and on suitable 

 stimulation others feel pain. Maps showing the distribution of 

 these four surface senses have been prepared in man, in whom 

 alone their differentiation is possible. There is no reason to 

 think that the same principle of distribution does not hold good 

 for the lower animals. 



Temperature-Sense. — Cold spots are more widely distributed 

 than warm, which suggests that it is more necessary that the 

 body should be made acquainted with the fact that it is cold 

 than that it is hot. The feeling of warmth or cold depends upon 

 the temperature of the skin, and not upon that of the body. 



Pressure-Sense. — The distribution of the spots is wider than 

 in those of the temperature-sense. The special nerve-endings 

 connected with pressure are found in a ring around the hair 

 follicles, in which position they are obviously most favourably 

 situated for stimulation through the hair itself. In the hairless 

 parts of the skin and muzzle special tactile corpuscles are found, 

 and in the horse special nerve-endings exist in the foot associated 

 with tactile sensibility. Tactile sensations play a very important 

 part in the lives of animals. In the lips and muzzle, which corre- 

 spond to the fingers of the biped, the touch organs proper are 

 located (p. 299) ; these parts are endowed with exquisite sensibility, 

 which enables the animal to be kept acquainted with the nature 

 of its surroundings and the character of its food. The long feelers 

 or hairs growing from the muzzle, face, and brow of the horse 

 are in connection with nerves in the skin, and are valuable for 

 tactile and consequently protective purposes. The ' cat hairs ' 

 on the general surface of the body are doubtless for the same 

 purpose. The tactile sensibility of the foot, by informing the 

 animal of the character of the ground it is travelling over, is 

 useful, though not absolutely essential, in locomotion ; nor is the 

 tactile sensibility in the foot of the horse absolutely essential to 

 its safety in progression, as is clearly proved by the results of 

 plantar neurectomy. 



Pain -Sense. —This is the most widely distributed of the 

 cutaneous senses. It is distributed in spots, probably supplied 

 by special fibres, though no special nerve-endings have been 

 determined. Pain confined to the surface of the body can be 

 readily located, but the localisation of interior pain is difficult ; 

 that of colic, for example, is referred to the abdominal wall. It 

 is supposed in man that the explanation of the difficulty in 



