582 THE SKIN AND ITS APPENDAGES [CH. XXXVIII. 



Large quantities of water, by raising the blood-pressure, increase 

 the perspiration. 



Some substances introduced into the body reappear in the sweat, 

 e.g., benzoic, tartaric, and succinic acids readily, quinine and iodine 

 with more difficulty. Compounds of arsenic and mercury behave 

 similarly. 



Diseases. Cystin has been found in some cases of cystinuria; 

 dextrose in diabetic patients; bile-pigment in those with jaundice 

 (as evidenced by the staining of the clothes); indigo in a peculiar 

 condition known as chromidrosis ; blood or haematin deriva- 

 tives in red sweat; albumin in the sweat of acute rheumatism, 

 which is often very acid; urates and calcium oxalate in gout; 

 lactic acid in puerperal fever, and occasionally in rickets and 

 scrofula. 



Kidney Diseases. The relation of the secretion of the skin to that 

 of the kidneys is a very close one. Thus copious secretions of urine, 

 or watery evacuations from the alimentary canal, coincide with dry- 

 ness of the skin ; abundant perspiration and scanty urine generally 

 go together. In the condition known as urcemia (see p. 556), when 

 the kidneys secrete little or no urine, the percentage of urea rises 

 in the sweat; the sputum and the saliva also contain urea under 

 those circumstances. The clear indication for the physician in 

 such cases is to stimulate the skin to action by hot-air baths and 

 pilocarpine, and the alimentary canal by means of purgatives. In 

 some of these cases the skin secretes urea so abundantly that when 

 the sweat dries on the body, the patient is covered with a coating of 

 urea crystals. 



Varnishing the Skin. By covering the skin of such an animal as 

 a rabbit with an impermeable varnish, the temperature is reduced, a 

 peculiar train of symptoms set up, and ultimately the animal dies. 

 If, however, cooling is prevented by keeping such an animal in warm 

 cotton-wool, it lives longer. Varnishing the human skin does not 

 seem to be dangerous. Many explanations have been offered to 

 explain the peculiar condition observed in animals ; retention of the 

 sweat would hardly do it ; the blood is not found post-mortem to 

 contain any abnormal substance, nor is it poisonous when transfused 

 into another animal. Cutaneous respiration is so slight in mammals 

 that stoppage of this function cannot be supposed to cause death. 

 The animal, in fact, dies of cold ; the normal function of the skin in 

 regulating temperature is interfered with, and it is animals with 

 delicate skins which are most readily affected. 



