520 OF SECRETION AND EXCRETION. 



quantity of malassimilated matter exists in the system, of which it is im- 

 portant to get rid. In many such cases, indeed, clinical observation had 

 already established the benefit derivable from such medicines, without afford- 

 ing the rationale of it. The urine as it is secreted trickles drop by drop into 

 the bladder, a musculo-membranous receptacle capable of holding from one to 

 three pints, from which it is discharged at stated periods. The bladder is com- 

 posed of two muscles opposed in action, the detrusor uriure, which forms the 

 greater part of the membranous bag, and the sphincter vesicse, which forms 

 its neck. Both are chiefly composed of unstriated muscular tissue, though 

 some fasciculi of striated muscle are found in the sphincter, and both are 

 under the governance of nervous centres situated in the lumbar portion of 

 the spinal cord, though they may also be influenced by the will. Under 

 ordinary circumstances the escape of the urine is prevented by the moderate 

 contraction or tone of the sphincter vesicre, to overcome which in the rabbit, 

 the pressure of a column of water of from 16 to 20 inches in height, 1 and in the 

 dog of about 30 inches (Giannuzzi and Nawrocki) is required. On section 

 of the lower part of the spinal cord, or of the vesical nerves, the pressure of 

 a column of water of only five or six inches in height is sufficient to force a 

 passage for the fluid through the sphincter. The concordant observations 

 of Masius 2 and Budge 3 show that the motor centre of the bladder is situated 

 at or about the level of the fourth lumbar Vertebra in animals. In connection 

 with the motor centre there appears to be a second or inhibitory centre also 

 situated in the lumbar region, for Goltz has shown 4 and observations on 

 man furnish corroborative evidence that neither incontinence nor retention 

 of urine need necessarily follow division of the- spinal cord ; but that in 

 some instances, the subjects of this injury can hold their water for several 

 hours, and discharge it at regular intervals that is to say, that whilst the 

 bladder is filling, some influence restraining the action of the detrusor is ex- 

 erted, which from analogy there is reason to believe proceeds from an inhib- 

 itory centre, till the excitation of the accumulated urine becomes so strong 

 as to stimulate the motor centre and overpower the inhibitory centre. Goltz 

 observed, and the experiment might be useful in cases of lesion of the spinal 

 cord in man, that the application of a cold wet sponge to the anus caused 

 immediate expulsion of the urine, either by stimulating the motor centre 

 and inducing contraction of the detrusor, or by paralyzing the inhibitory 

 centre, and thus effecting the relaxation of the sphincter, and removing any 

 obstacle to the respondence of the detrusor to the stimulus of the moderate 

 accumulation of urine in the bladder. Daily experience teaches that the 

 will can exert an influence both on the motor and inhibitory centres situated 

 in the lumbar region of the cord. 



4. Of the Skin Cutaneous Transpiration. 



419. The Skin is the seat of various secretions, as the Sebaceous, Ceru- 

 minous, and Odoriferous, for each of which it is provided with special 

 organs; but these have reference chiefly to its own protection, or to some 

 other local purpose; and the only one which can be regarded as truly cxcre- 

 mentitious, is the Transpiration of aqueous fluid holding certain matters in 

 solution. The elimination of this fluid from the blood is effected by the Su- 

 doriparous glanduho (Fig. 182), which essentially consist of long convoluted 

 tubes (a, a), rarely single, but usually multiplied by repeated dichotomous 



1 Kupressow, Pfliiger's Archiv. 1872, Bd. v, p. 291. 



2 Bulletin de 1'Acad. Roy. do Belgiquc, 1868, p. 491. 



3 Yiivhow's Archiv, 1858, Bd. xv, p. 115. 



4 Tiiuger's Archiv, 1873, p. 474. 



