162 CHANGES OF AIR AND BLOOD IN RESPIRATION. 



quantity of oxygen is absorbed by the skin of the human subject, and a quan- 

 tity of carbon dioxide, which is relatively larger, is exhaled. Exhalation of 

 carbon dioxide, which is connected with the uses of the skin as a general 

 eliminating organ and is by no means an essential part of the respiratory 

 process, will be more fully considered in connection with the physiology of 

 excretion. Carbon dioxide is given off with the general emanations from the 

 surface, being found, also, in solution in the urine and in most of the secre- 

 tions. It is well known that death follows the application of an imperme- 

 able coating to the entire cutaneous surface ; but this is by no means due to a 

 suppression of its respiratory office alone. The skin has other uses, particu- 

 larly in connection with regulation of the animal temperature, which are 

 much more important. 



An estimate of the extent of the cutaneous, as compared with pulmonary 

 respiration, has been made by Scharling, by comparing the relative quantities 

 of carbon dioxide exhaled in the twenty-four hours. According to this ob- 

 server, the skin performs fa to ^V of the respiratory office. It is difficult to 

 collect all the carbon dioxide given off by the skin under perfectly normal 

 ' conditions. In the observations by Aubert, the estimate is very much lower 

 than that given by Scharling. 



ASPHYXIA. 



The effects of cutting off the supply of oxygen from the lungs are mainly 

 referable to the circulatory system and have already been considered in treat- 

 ing of the influence of respiration upon the circulation. It will be remem- 

 bered that in asphyxia the unaerated blood passes with so much difficulty 

 through the systemic capillaries as finally to arrest the action of the heart. 

 It is the experience of experimenters on living animals, that the movements 

 of the heart, once arrested in this way, can not be restored ; but that while 

 the slightest regular movements continue, the heart's action will gradually 

 return if air be re-admitted to the lungs. 



A remarkable power of resisting asphyxia exists in newborn animals 

 that have never breathed. This was noticed by Haller and others and has 

 been the subject of many experiments. Legallois found that young rabbits 

 would live for fifteen minutes deprived of air by submersion, but that this 

 power of resistance diminished rapidly with age. W. F. Edwards has shown 

 that there exists a great difference in this regard in different species. Dogs 

 and cats, which are born with the eyes shut and in which there is at first a 

 very slight development of animal heat, will show signs of life after submer- 

 sion for more than half an hour ; while Guinea-pigs, which are born with 

 the eyes open, are much more active and produce a greater amount of heat, 

 will not live for more than seven minutes. The explanation of this is that 

 in most warm-blooded animals, during the very first periods of extraiiterine 

 life, the demands on the part of the system for oxygen are comparatively 

 slight. At this time, there is very little activity in the general processes of 

 nutrition and in the consumption of oxygen and the exhalation of carbon 

 dioxide. The actual difference between the consumption of oxygen imme- 



