488 EESPIEATIOX. 



efforts take place. Respiratory 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 armiii occasionally finds its way into the respira- 

 tory passages of the foetus, where it could only enter in efforts 

 at respiration. Winslow, in the latter part of the last cen- 

 tury, first noticed .respiratory efforts in the foetuses of cats 

 and dogs, in the uterus of the mother during life ; 1 and many 

 others have observed that when foetuses are removed from 

 vascular connection with the mother, they will make vigor- 

 ous efforts at respiration. This fa'ct we have frequently 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 follow- 

 ing each other at regular intervals, independently of irritation 

 of the general surface. 2 



From what has been experimentally demonstrated with 

 regard to the location 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 the 

 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 



1 British and Foreign Medico- Chirurgical Review, April, 1864, p. 330. 



2 We take from our note-book the following observation showing respiratory 

 efforts in a very young animal : 



" Jan. 6, 1865. In operating to-day on a small-sized bitch, for the purpose of 

 demonstrating the glycogenic process in the liver, I found her pregnant, and in 

 the uterus were six pups, certainly not more than one-fourth the size which they 

 attain before birth. (They were four inches long.) On removing them from the 

 womb, and dividing the umbilical vessels, they all made a number of profound 

 respiratory efforts at intervals of from two to three minutes." 



