168 KESPIEATIOK 



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. 

 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. Eespiratory 

 movements will take place, however, even in very young animals, when there is a defi- 

 ciency 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 respiration. Winslow, in the latter part of the last century, first noticed respir- 

 atory 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 mother, they will make vigorous efforts at respiration. This fact we have fre- 

 quently had occasion to demonstrate in making operations upon pregnant animals. After 

 the death of the mother, the foetus always makes a certain number of respiratory efforts, 

 which are not uncertain in their character, but distinct, accompanied by great elevation 

 of the ribs, opening of the mouth, and following each other at regular intervals, inde- 

 pendently of irritation of the general surface. 



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 conveyed 

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

 to an accumulation of carbonic acid in the lungs and is entirely consistent with our 

 views, locating the respiratory sense in the general system. 



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. Carbonic 

 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 -fa to -fa 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- 



