426 PHYSIOLOGY. 



the larger glands are arranged longitudinally along the tube. Be- 

 yond the muscular coat is the basement-membrane ; so that the duct 

 has a definite outline and exists as an entity that is distinct from 

 the surrounding tissues. 



The distal portion of the tube serves the simple purpose of a 

 conduit for the passage of the sweat-secretion to the skin surface. 

 It contains no muscular fibers or basement-membrane. There is, 

 however, a distinct lumen surrounded by several layers of cubical 

 cells; so that by some authorities this portion of the apparatus is 

 considered to be but an opening between epidermal cells. 



Glands which are constantly active, as are the sweat-glands, 

 must necessarily require a very liberal blood-supply. Each coil (the 

 real seat of secretion) is surrounded by a network of capillaries, 

 whose arrangement is such that the secretory cells are easily enabled 

 to obtain the watery secretion from the blood-stream. 



Nerves. A plentiful supply of nerve-fibers in the form of a 

 nerve-plexus ends in the glandular substance. That the secretion of 

 sweat is not a mere filtration that varies according to the blood- 

 pressure, but a process dependent upon a direct action of the nerve 

 upon the gland-cell, has been demonstrated by Ott. In experiments 

 upon cats certain changes were produced in the cell-protoplasm by 

 changes in the activity of the nerve. 



In the cat the sciatic was cut and the animal kept until the 

 fifth day. At this time the pads of the feet were excised, placed in 

 absolute alcohol, and when hard enough were cut into sections, 

 stained with carmine solution, and mounted in glycerin. 



In another cat the sciatic was exposed and the nerve feebly 

 irritated for a period of two and one-half hours, when the pads of 

 the feet were treated in the same manner. 



Sections of the pads of the feet of each cat were then examined 

 microscopically. It was found that the irritated cells were smaller 

 than the resting cells, that their protoplasmic contents were more 

 granular and more highly tinged with carmine solution, although 

 left in it the same length of time as 'the resting cell. These facts 

 have been confirmed by Renaut in the horse's glands. 



Sweat is the secretory product of the sudoriferous glands. It 

 is discharged in a continuous fashion upon the surface of the skin, 

 there to be gotten rid of as vapor. As long as the secretion is small 

 in amount it is evaporated from the surface at once. Because of 

 this feature it is termed insensible perspiration. The skin is supple, 

 fresh, and without any appreciable humidity. 



