EXCRETION 471 



jacral region of the spinal cord and pass to their destination by two paths, 

 f he fibers in the first path leave the spinal cord by way of the second to the 

 ifth lumbar nerves, then pass into and through the sympathetic chain, 

 hrough the inferior splanchnics to the inferior mesenteric ganglion around 

 he cells of "which their terminal branches arborize; from the cells of this 

 janglion new fibers emerge which pass through the hypogastric nerves to the 

 nuscles. The fibers of the second path leave the spinal cord by way of the 

 iecond to the fourth sacral nerves, then pass into the pelvic or erigens nerve 

 o small ganglia (pelvic ganglia) along the sides of the bladder around the 

 :ells of which their terminal branches arborize; from the cells of these ganglia 

 ^iew nerve-fibers emerge which pass directly to the muscles. In both paths 

 :he nerves coming from the cord are pre-ganglionic, those coming from the 

 ganglia, post-ganglionic. 



The central mechanism that excites and coordinates the activities of the 

 vesical muscles is situated in the lumbo-sacral region of the spinal cord and 

 ! .s designated the vesical or urination center. 



Afferent Nerves The afferent nerve-fibers that excite the central mech- 

 inism to activity, are contained in both the nerve-paths described in fore- 

 going paragraphs and enter the spinal cord in the dorsal roots of the lumbar 

 ind spinal nerves. 



Though the origin, course and distribution of the nerves composing this 

 mechanism are fairly well known, their mode of action is somewhat obscure 

 and the results of experimentation not always in accord. According to v. 

 Zeissl stimulation of the peripheral ends of the divided hypogastric nerves 

 causes mainly a contraction of the sphincter muscles and a relaxation of the 

 detrusor muscle, while a stimulation of the peripheral ends of the divided 

 sacral nerves causes a vigorous contraction of the detrusor muscle and a re- 

 laxation of the sphincter muscles. The lumbar centers would therefore 

 cause a reception and a retention of the urine, and the sacral centers would 

 cause its expulsion. 



PERSPIRATION. SEBUM 



The perspiration or sweat, the chief secretion of the skin, is a clear colorless 

 fluid, slightly acid in reaction and saline to the taste. Its specific gravity 

 varies from 1.003 to 1.006. Unless collected from the soles of the feet and 

 the palms of the hand, it is apt to be mixed with epithelial cells and sebum 

 The total quantity of perspiration secreted daily has been variously estimated 

 at from 700 to 1000 grams; the exact amount, however, is difficult of determi- 

 nation, for the reason that the rate of secretion varies greatly with variations in 

 temperature, food, drink, season of the year, etc. 



Chemic analysis of the sweat shows that it contains but from 0.5 t< 

 per cent, of solid constituents, the variation in the percentage depending on 

 the quantity of water secreted. The solids consist of traces of urea, neutral 

 fats, lactic and sudoric acids in combination with alkaline bases, and inorganic 

 salts (Fovel). Other observers, however, have not been able to detect the 

 presence of either lactic or sudoric acid. Urea is a constant ingredient, 

 though its percentage is extremely small, possibly not more than o.i per 

 cent The amount, however, may be very much increased in uremic 

 conditions, the result of acute or chronic disease of the kidneys The inor- 

 ganic constituents consist mainly of sodium chlond and alkaline and 



