168 RESPIRATION. 



statements of those who have been unable to note any difference in color between the 

 blood contained in the umbilical arteries and the vein, there are direct observations 

 showing that such a difference does exist. Legallois frequently observed a bright-red 

 color in the blood of the umbilical vein ; and, on alternately compressing and releasing the 

 vessel, he saw the blood change in color successively from red to dark and from dark to red. 

 Zweifel has demonstrated the presence of oxyhsemaglobine in the blood of the umbilical 

 vessels by means of the spectroscope, thus showing that it contains oxygen. As oxygen is 

 thus adequately supplied to the system, the foetus is in a condition similar to that of the 

 animals in which artificial respiration was effectually performed. The want of oxygen is 

 fully met, and therefore no respiratory efforts take place. Respiratory movements will 

 take place, however, even in very young animals, when there is a deficiency of oxygen 

 in the system. It has been observed that the liquor amnii occasionally finds its way into 

 the respiratory passages of the foetus, where it could only enter during efforts at respira- 

 tion. Winslow, in the latter part of the last century, first noticed respiratory efforts in 

 the foetuses of cats and dogs in the uterus of the mother during life ; and many others 

 have observed that, when foetuses are removed from vascular connection with the moth- 

 er, they w r ill make vigorous efforts at respiration. This fact we have frequently had oc- 

 casion to demonstrate in making operations upon pregnant animals. After the death of 

 the mother, the foetus always makes a certain number of distinct and unmistakable respi- 

 ratory efforts, which follow each other at regular intervals. 



From what has been experimentally demonstrated with regard to the seat and cause 

 of the respiratory sense after birth, it is evident that want of oxygen is the cause of re- 

 spiratory movements in the foetus. When the circulation in the maternal portion of the 

 placenta is interrupted from any cause, or when the blood of the foetus is obstructed in 

 its course to and from the placenta, the impression due to want of oxygen is made upon 

 the medulla oblongata, and efforts at respiration are the result. This cannot be due to 

 an accumulation of carbonic acid in the lungs, and it is entirely consistent with our views 

 with regard to the seat of the respiratory sense. 



Cutaneous Respiration. 



This mode of respiration, although very important in many of the lower orders of ani- 

 mals, is insignificant in the human subject and is even more slight in animals covered 

 with hair or feathers. Still, an appreciable quantity of oxygen is absorbed by the skin 

 of the human subject, and an amount of carbonic acid, which is proportionately larger, 

 is exhaled. Exhalation of carbonic acid, which is connected rather with the functions 

 of the skin as a general eliminating organ and is by no means an essential part of the re- 

 spiratory process, will be more fully considered under the head of excretion. Carbonio, 

 acid is given off with the general emanations from the surface, being found at the same 

 time in solution in the urine and in most of the secretions. It is well known that death 

 follows the application of an impermeable coating to the entire cutaneous surface ; but 

 this is by no means due to a suppression of its respiratory function alone. The skin has 

 other offices, particularly in connection with regulation of the animal temperature, which 

 are infinitely 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 carbonic acid exhaled 

 in the twenty-four hours. According to this observer, the skin performs from ^ to r of 

 the respiratory function. It is exceedingly difficult to collect all the carbonic acid given 

 off by the skin under perfectly normal conditions. In some recent observations by Au- 

 bert, 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 under the head of the influ- 



