CUTANEOUS RESPIRATION 299 



who found a marked increase in the rate of blood-flow through the 

 hands, associated with an acceleration of the heart beat, dilatation of 

 the arterioles and a fall in the venous pressure. In ' aviator's sick- 

 ness ' the essential factor is also oxygen deficiency. 



SECTION IX. CUTANEOUS RESPIRATION. 



It has already been remarked that a frog survives the loss of its lungs 

 for some time, respiration going on through the skin. Indeed, it has 

 been calculated that in the intact frog, under ordinary conditions, as 

 much as three-quarters of the total gaseous exchange may be cutaneous. 

 Two frogs were seen to live thirty- three days, and one even forty days, 

 after excision of the lungs. The effect of exclusion of the pulmonary 

 respiration on the gaseous exchange depends on the previous intensity 

 of the metabolism. If this is high the gaseous exchange sinks markedly ; 

 if it is low there is scarcely any alteration. At their maximum efficient y, 

 the frog's lungs are capable of sustaining a much greater exchange 

 than the skin. Besides this quantitative, there is a qualitative differ- 

 ence, the carbon dioxide passing more easily through the skin than the 

 oxygen, so that the respiratory quotient is increased by elimination of 

 the lungs. In mammals the structure of the skin is different, and 

 respiration can only go on through it to a very slight extent. The 

 amount of carbon dioxide excreted in man, although only about 4 grm. 

 or 2 litres in twenty-four hours, is much greater than corresponds to 

 the quantity of oxygen absorbed through the skin. It has been as- 

 serted, and no doubt with justice, that some at least of the carbon 

 dioxide given off is due to putrefactive processes taking place on the 

 surface of the body. Such processes, as has already been pointed out, 

 seem also responsible in part for the heavy odour of a ' close ' room. 

 For no harmful products appear to be exhaled from the skin when it is 

 properly cleansed. In spite of the romantic statements to the con- 

 trary in ancient and modern books (for instance, the story of the child 

 that was gilded to play the part of an angel at the coronation of a 

 medieval pope, but died before the ceremony began), the whole of the 

 human skin may be coated with an impermeable varnish without any 

 ill effects. The entire surface of the body of a patient with cutaneous 

 disease was covered with tar, and kept covered for ten days. There was 

 not the least disturbance of any normal function. The serious effects 

 of varnishing the skin in animals are due, not to retention of poisonous 

 substances, but to increased heat loss. Varnishing is not so rapidly 

 harmful in large animals like dogs as in rabbits, which have a relatively 

 great surface and a delicate skin. The danger of widespread superficial 

 burns is well known. But it is not due to diminished excretion by the 

 skin, for death occurs when large cutaneous areas remain uninjured. 

 The patient nearly always dies when a quarter of the whole skin is 

 burnt; yet the remaining tl.ree-quarters may surely be considered 

 capable, from all analogy, of making up the loss by increased activity. 

 One kidney is enough to eliminate the products of the nitrogenous 

 metabolism of the whole body. It is difficult to see why the excretion 

 of the trifling amount of solid matter in the perspiration should be 

 interfered with by the loss of 25 per cent, of the sweat-glands. The real 

 explanation of the serious effects of extensive superficial burns is 

 perhaps the excessive irritation of the sensory nerves, which may lead 

 to changes in the nervous centres, or reflexly in other organs, or the 

 chemical changes in the damaged tissue, for example, in the blood- 

 corpuscles, or the transudation of lymph at the injured part, and con- 

 sequent increase in the concentration of the blood. 



