SECRETIONS 109 



the blood in too large quantities (e.g. many salts, grape- 

 sugar in ease of glycosuria), also substances normally not 

 found in the body (e.g. drugs, such as potassium iodide, 

 salicylic acid, santonin, etc.). 



4. Micturition. The urine is driven from the urinary 

 tubules into the pelvis by the pressure of the secretion. 

 From the pelvis the urine is forced by the peristaltic contrac- 

 tions of the two ureters into the bladder. The bladder is 

 closed by the tonic contraction of the sphincter vesicae. 

 During micturition, the tonus of the sphincter is inhibited 

 and the contraction of the detrusor urinse diminishes the 

 compass of the bladder. The muscles of the bladder are 

 supplied with nerves from the sacral and lumbar nerves and 

 from the sympathetic. Their centre lies in the lumbar cord. 



8. THE SECRETION OF SWEAT 



1. Composition of sweat. Sweat is a clear, colorless fluid 

 having a specific gravity of 1.003-1.006. Its reaction may 

 be acid, neutral or alkaline; it has a salty taste and charac- 

 teristic odor. It contains 0.850.91$ solids which include 

 0.65$ salts (chiefly NaCl) and 0.24$ organic substances 

 (0.12$ urea). The amount daily secreted is very variable. 

 The secretion of sweat is closely related to the regulation of 

 temperature (see Chapter XIII). 



2. Secretion of sweat. The sudoriferous glands are long 

 unbranching tubules which form at the lower end a globular 

 mass (0.30.7 mm in diameter) composed of a coiled tube. 

 The walls of these coiled tubules have a single layer of 

 cuboidal cells. 



The sweat secretion is dependent upon the nervous system. 

 Stimulation of the sciatic or brachial nerve of a Qat produces -^^ 

 sweating of the paw. It is not mere filtration of the blood v 

 fluid, but depends upon the specific activity of the gland, as 

 the following facts show. Secretion of sweat does not take 

 place continuously, and twenty minutes after the amputation 

 of a limb, stimulation of the nerve still produces perspiration. 



