406 STUDIES IN ADVANCED PHYSIOLOGY. 



deeper portions of the corium, or more generally in the sub- 

 cutaneous tissue. From this coil a tubular duct runs 

 through the corium and epidermis, carrying its secretions 

 to the surface of the skin. Instead of running directly up- 

 wards the duct winds through the corium and epidermis in 

 a spiral cork-screw fashion. A cross-section of the tube of 

 this gland shows it to be composed of an investment of con- 

 nective tissue and an inner layer of columnar cells enclosing 

 the lumen. The coiled portion of the tube in the sub- 

 cutaneous tissue is richly supplied with blood-vessels and 

 nerves. The reason for this coiling of the tube is no doubt 

 explained in the saving of space. The explanation of the 

 spiral winding of the duct through the skin is not apparent. 

 These glands are especially plentiful on the forehead 

 and under the arms. Rough calculations have placed the 

 number of sweat glands on the entire body at about 2,000,- 

 000. 



1. Nerves. That these glands are under the control of 

 the nervous system is beyond question. It is an every-day 

 observation that states of emotion, fright or pain directly 

 affect the perspiration of the body and thus clearly point 

 to the existence of sweat centers in the spinal cord and 

 brain. But evidence still more direct is at hand. It is 

 possible to amputate a limb of a cat, for instance, and by 

 stimulating the sciatic nerve, along which the sweat fibers 

 run, to produce droplets of sweat on the balls of the feet, 

 and this even when there is no increase in the blood supply ; 

 in fact, when the circulation has entirely stopped. This is 

 conclusive proof that the process of sweating is not a sim- 

 ple filtration of water and salt from the lymph or blood in 

 and through these glands, but that it is a physiological 

 phenomenon under direct nervous control, and to a large 

 extent independent of vascular conditions. 



Experiments seem to point to the existence of lower 

 sweat centers in the spinal cord which may, however, under 

 special conditions be controlled by higher centers in the 



