364 PHYSIOLOGY CHAP. 



of blood circulating, producing pallor and coldness in the corre- 

 sponding cutaneous regions ; their relaxation has the opposite effect. 



(/3) The muscle fibres of the hair follicles, whose contraction 

 produces " goose skin." The study of the innervation of these 

 organs, which are specially developed in the cat, provided Langley 

 with a means of determining the arrangement and distribution 

 of the sympathetic fibres. He found, however (1904), that in this 

 animal the conditions were more complex than in the other 

 mammals, as there are two sets of antagonist muscles, one of 

 which, the more powerful, prevails over the other in artificial 

 stimulation, and causes depression of the hairs, while the other 

 causes their erection. In man, owing to the retrogression of 

 the piliferous system, the muscles of the hair follicles are of no 

 great importance. Erection of the hairs produces "goose skin" 

 after stimulation by cold and in certain emotions, as fear, etc. 



(y) The ducts of certain cutaneous glands, e.g. the mammary 

 glands, are provided with contractile elements, which are con- 

 trolled by the sympathetic system. 



The different glands of the skin, in particular the sweat glands 

 and sebaceous glands, are also innervated by the sympathetic. 



The second large and important province governed almost 

 exclusively by the sympathetic system includes the visceral 

 organs in the strict sense, viz. the organs of circulation (heart, 

 Hood- and lymph-vessels) ; and the digestive system, both its 

 unstriated muscles on which the co-ordiuated movements of the 

 stomach and intestines, defaecation, micturition, etc., depend and 

 its secretory glands. 



On the following page is Langley 's Table l with a few minor 

 alterations. It sums up the various functions of the sympathetic 

 system in its widest sense. 



III. The first problem to be studied in the physiology of the 

 sympathetic nervous system is its intimate structure, the origin 

 and course of its nerve-fibres, and the relations in which these 

 stand with the several ganglia. 



As we know, two different experimental methods can be 

 utilised in tracing the course of the nerve-fibres ; one anatomical, 

 based on Waller's law (p. 233), according to which the part of 

 the nerve that is severed from its trophic centre degenerates ; 

 the other, physiological, based on the phenomena which appear 

 on exciting the central or peripheral end of the cut nerve, or the 

 functional disturbances seen after the cutting, cooling, poisoning, 

 etc., of the nerve. 



We must first consider the origin and course of the efferent 

 nerve-fibres (motor or secretory). 



The only path followed by the nerve-fibres which connect the 

 cerebrospinal axis with the ganglion chain of the sympathetic, 



1 Langley, Ergebnisse der Physiologic, 1903, Jahrgang ii. Abteilung ii. p. 830. 



