CUTANEOUS RESPIRATION 293 



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 tLree-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. 



PRACTICAL EXERCISES ON CHAPTER IV. 



i. Tracing of the Respiratory Movements in Man. Pass a tape 

 through the rings B of the stethograph shown in Fig. 134, and 

 then around the neck or over the shoulders, so as to support the 

 instrument on the chest at a convenient height. Fasten tapes to the> 

 hooks and tie them by a slip-knot round the chest. The tube E is 

 connected to a recording tambour, writing on a drum. Or use the belt 

 stethograph or spirograph of Fitz (p. 232), fastening the elastic tube 

 round the chest with the chain, and connecting it with a tambour or 

 the bellows recorder shown in Fig. 137. Compare the extent of the 

 excursion when the tube is adjusted at different levels over the thorax 

 and abdomen. 



