RESPIRATORY EFFORTS BEFORE BIRTH. 161 



ciency in haematosis, either from a vitiated atmosphere, mechanical obstruc- 

 tion in the air-passages or grave trouble in the general circulation, produces 

 all grades of sensations, from the slight oppression which is felt in a crowded 

 room, to the intense distress of suffocation. When haematosis is but slightly 

 interfered with, only an indefinite sense of oppression is experienced, and the 

 respiratory movements are a little increased, the most marked effect being 

 an increase in the number and extent of sighing inspirations. 



RESPIRATORY EFFORTS BEFORE BIRTH. 



It is generally admitted that one of the most important uses of the pla- 

 centa, and the one which is most immediately connected with the life of the 

 foetus, is a respiratory interchange of gases, analogous to that which takes 

 place in the gills of aquatic animals. The placental villi are bathed in the 

 blood of the uterine sinuses, and this is the only way in which the foetal blood 

 can receive oxygen. Legallois 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 oxyhaemaglobine 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 sys- 

 tem, the foetus is in a condition similar to that of the animals in which arti- 

 ficial 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 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 enter only during efforts at respiration. 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 mother, they 

 make vigorous efforts at respiration. After the death of the mother, the 

 foetus always makes a certain number of distinct and unmistakable respiratory 

 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 oxy- 

 gen is the cause of respiratory 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 pla- 

 centa, the impression due to want of oxygen is made upon the medulla oblon- 

 gata, and efforts at respiration are the result. 



CUTANEOUS RESPIRATION. 



Respiration by the skin, although very important in many of the lower 

 forms of animals, is inconsiderable in the human subject and is even more 

 insignificant in animals covered with hair or feathers ; still, an appreciable 



