276 A MANUAL OF PHYSIOLOGY 



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

 exchange than the skin. Besides this quantitative, there is a 

 qualitative difference, 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 asserted, 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 contrary 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. Trie 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 wide- 

 spread 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 three- 

 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 ex- 

 cessive 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 consequent 

 increase in the concentration of the blood. 



Voice and Speech. 



Voice. Sounds of various kinds are frequently produced by 

 the movements of animals as a whole, or of individual organs. 

 The muscular sound, the sounds of the heart and of respiration, 

 we have already had to speak of. Such sounds may be considered 

 as purely accidental as the footfall of a man or the buzzing of a 

 fly. The wings of an insect beat the air, not to cause sound, but 

 to produce motion ; the respiratory murmur is a mere indication 

 that air is finding its way into the lungs, it is in no way related 



