RESPIKATOEY EFFORTS BEFOEE BIKTH. 487 



servative provision of Nature, by which faintness and dimi- 

 nution in the force of the heart's action favor the arrest of 

 the flow of blood. 



Poisoning by carbonic oxide is generally accompanied with 

 convulsions, which arise from the sense of suffocation, and are 

 due to a fixation of this gas in the blood-corpuscles, by which 

 they are rendered incapable of giving oxygen to the system. 

 Convulsions also attend poisoning by hydrocyanic acid, in 

 cases in which the system is not overpowered immediately by a 

 large dose of this agent, and the muscular irritability destroyed. 



Experiments have failed to show that the respiratory 

 sense, or the sense of suffocation, is due to irritation produced 

 by carbonic acid in the non-oxygenated blood. 



Respiratory Efforts ~before Birth. 



It is generally admitted that one of the most important 

 functions of the placenta, and the one which is most im- 

 mediately connected with the life' of the foetus, is a respira- 

 tory interchange of gases, analogous to that which takes 

 place in the gills of aquatic animals. The vascular pro- 

 longations from the foetus are continually bathed in the 

 blood of the mother, and this is the only way in which it 

 can receive oxygen. Notwithstanding the 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 alter- 

 nately compressing and releasing the vessel, he saw the blood 

 change in color successively from red to dark, and dark to 

 red. 1 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 



1 BERARD, Cours de Physiologic, tome Hi., p. 422. 



