RESPIRATION. 795 



creased by exercise. The quantity of nitrogenous matter daily re- 

 moved in the shape of desquamated epidermic cells, is said to be about 

 11 grains. A partial interference with the excretory function of the 

 skin, causes headache, lassitude, and febrile reaction ; a more serious 

 disturbance, by over-exciting the kidneys, will bring on temporary 

 albuminuria. 



The preceding facts sufficiently explain the high importance of 

 cleanliness of the skin, for the preservation, not only of comfort, but 

 of health. Daily ablutions by sponging, and the occasional use of the 

 tepid bath, are of great efficacy in the maintenance of a pure condition 

 of the blood. 







The Cutaneous Excretion in Animals. 



The sudoriferous glands of the higher Yertebrata, and the cutaneous gland- 

 ular organs of the lower Vertebrate, and Non-vertebrate animals, have been 

 already described (p. 372). 



When the skin of a rabbit is shaved, and the body subsequently coated over 

 with varnish impenetrable to water and gases, death ensues from asphyxia in 

 from six to twelve hours, a condition which has been named cutaneous asphyxia. 

 The symptoms are depression, difficulty of breathing, lowering of the tempera- 

 ture, congestion of the tissues and organs with dark blood, and ultimate death. 

 The arrest of cutaneous respiration may partly account for this form of death, 

 with accumulation of carbonic acid in the blood ; but doubtless also, it depends 

 on the shutting in of peculiar cutaneous products. The fatal result can scarcely 

 be referred to the non-exhalation of water. In the soft-skinned Amphibia, the 

 entire cutaneous surface exhales carbonic acid, and absorbs oxygen ; in the 

 frog, for example, after removal of the lungs, 5 cubic inch of carbonic acid gas 

 has been excreted from the skin, in eight hours. (Bischotf.) This experiment 

 is performed by putting the animal, after deprivation of its lungs, under a 

 glass receiver tilled with air, and placed over mercury ; the carbonic acid is 

 absorbed by lime-water, and so measured. The skin of the .frog, which is 

 moist and full of capillary vessels, presents conditions favorable to the solution 

 and diffusion of gases in contact with it, by a mechanism to be explained in 

 the next Section. Probably nearly as much carbonic acid is eliminated by the 

 frog, from its cutaneous surface, as from its comparatively simple lungs. 



In the soft-skinned, aquatic, Non-vertebrate animals, the integument is 

 often an adjuvant, or the chief, or sole, respiratory surface, being for that pur- 

 pose frequently ciliated. 



RESPIRATION. 



The arterial blood in passing through the systemic capillaries, serves 

 the purposes of nutrition, stimulation, secretion, and excretion, and 

 the blood, as it leaves those capillaries, is tainted by the products of 

 venous absorption. In the various changes which it undergoes, the 

 arterial blood both loses and acquires certain substances, and so be- 

 comes venous. Thus changed, it returns to the heart, and, being now 

 conveyed through the pulmonary capillaries, is there rapidly restored 

 to its arterial condition. This conversion of venous into arterial blood, 

 is the immediate object of the respiratory process. In it, oxygen is 

 absorbed by the blood, whilst carbonic acid, together with some, watery 

 vapor, is given off. The source of the oxygen is the atmosphere ; the 



