CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 727 



Hairs have of course functions of far greater importance than 

 that served by their connection with the sebaceous glands ; they 

 afford protection to the body and in many cases act as sense organs. 

 And we may here turn aside from the theme in hand tcr call 

 attention to the muscle, arrector pili, with which in many cases 

 the hair is provided. From the dermis on the side to which the 

 hair slopes, for most of the hairs are inserted in a sloping fashion, 

 a band of plain muscular fibres slants down to the hair and is 

 attached to the hair follicle at a little distance below the mouths of 

 the sebaceous glands. The contraction of this muscle tilts up the 

 sloping hair or in other words erects it. 



Experiments on such animals as cats have shewn that fibres 

 carrying motor impulses to these muscles, pilomotor fibres, leaving 

 the spinal cord by the anterior roots of spinal nerves, pass by the 

 white rami communicantes to the sympathetic chain, and thence 

 having run a shorter or longer course in that chain, return by the 

 grey rami to the spinal nerves and so reach the skin ; their path in 

 fact is in a broad way similar to that of the vaso-constrictor 

 fibres distributed to the skin. When an animal, excited by fear or 

 anger, " bristles " the hairs of this or that part of its body, pilomotor 

 impulses started in the central nervous system by the emotion, 

 follow the path just described. And the so-called "goose skin" 

 which in ourselves is brought about by the contraction of plain 

 muscular fibres distributed in the dermis independent of hairs, is 

 the result of the action of a similar nervous mechanism. The 

 nicotin method ( 169) shews that the pilomotor fibres leaving the 

 central nervous system end in connection with cells at some point 

 or other of the sympathetic system, from which point other fibres 

 carry on the impulses to the arrector muscles. At this point in 

 fact there is a relay, so that the connection of the arrector pili with 

 the central nervous system is an indirect one, not a direct one as 

 is the case with a skeletal muscle. 



