TOUCH. 361 



the pith or not, though of course non-vascular, is probably permeable 

 to nutrient fluids, which nourish the hair. It is supposed that the 

 sudden whitening of the hair from grief, fear, or intense mental ex- 

 citement, is due to certain changes in the pith, produced through the 

 blood. 



Many of the unstriped muscular fibres, which, as before stated, are 

 found in the substance of the true skin, pass obliquely down from the 

 surface of the cutis, to the under side of the slanting hair follicles. It 

 is the contraction of these fibres, which erects the hairs, by causing them 

 to assume a vertical direction, and which, by drawing the follicles to the 

 surface, and pulling in a little point of the skin, produces that rough- 

 ness of the integument, generally called horripilation, goose's skin, or 

 cutis anserina. The standing on end of the hair of the head, as the 

 result of extreme fright, may be partly due to the contraction of such 

 fibres, but it must also be dependent on the action of the occipito-fron- 

 talis muscle. 



The sebaceous or fat-forming glands, Fig. 69, a, 4, from sebum, fat, 

 are situated in the cutis, and exist in great numbers associated with 

 the hairs, there being usually two for each hair follicle. Those of the 

 larger hair follicles average about ^th of an inch in width. They are 

 proper appendages of the hair follicles, and are not found in the palms 

 and soles, where no hairs exist. Each gland is a flask-shaped body, 

 composed of from five to twenty little sacs, clustered around and lead- 

 ing into a common duct, which almost always opens into a hair follicle, 

 each follicle receiving one or more ducts ; sometimes, however, the 

 ducts of the glands open upon the cutaneous suface. These glands are 

 lined throughout by a fine epithelium, and their unctuous secretion 

 first anoints the hair bulb, and then oozes out upon the stem and the 

 neighboring surface of the cuticle, which it prevents from getting dry 

 and cracked. On the nose and face the sebaceous glands are of con- 

 siderable size. The Meibomian glands in the eyelids are large seba- 

 ceous glands. 



The sudoriferous glands or sweat glands, Fig. 66, 5, will be described 

 in the Section on Excretion. 



Touch. 



The modification of the sensory power by which the shape, size, 

 solidity and other mechanical properties or qualities of objects are dis- 

 tinguished, constitutes the sense of touch or tact, or the tactile sense. 

 The sense of temperature is also usually referred to this sense ; and so 

 likewise are the feelings of pain or its opposite. So far as is yet known 

 the peripheral sensory organs and the nerve-fibres concerned in all 

 these forms of sensation are the same. But, as already mentioned 

 (p. 271), different paths in the spinal cord are supposed to be pursued 

 by tactile, thermal, and painful impressions ; and instances are recorded 

 in which the sense of touch was lost, whilst that of temperature re- 

 mained. As to the exact sensorial centres excited in each case, nothing 

 is positively determined. 



The simplest impression conveyed to the mind by the tactile sense 



