ASPHYXIA. 



169 



ence of respiration upon the circulation. It will be remembered that, in asphyxia the 

 non-aerated blood passes with so much difficulty through the systemic capillaries as 

 finally to arrest the action of the heart. It is the experience of those who have experi- 

 mented on this subject, that the movements of the heart, once arrested in this way, can- 

 not be restored, but that while the slightest regular movements continue, its functions 

 will gradually return if air be readmitted to the lungs. 



A remarkable power of resisting asphyxia exists in newly-born animals that have 

 never breathed. This was noticed by Haller and others and has been the subject of nu- 

 merous experiments, among which we may mention those of Buffon, Legallois, and W. F. 

 Edwards. Legallois found that young rabbits would live for fifteen minutes deprived of 

 air by submersion, but that this power of resistance diminished rapidly with age. W. 

 F. Edwards has shown that there exists a great difference in this regard in different 

 classes of animals. Dogs and 'cats, which are born with the eyes shut and in which there 

 is at first a very slight development of animal heat, will show signs of life after submer- 

 sion for more than half an hour ; while Guinea-pigs, which are born with the eyes open, 

 are much more active, and produce a greater amount of heat, will not live more than 

 seven minutes. The cause of this peculiarity has been attributed to the existence of 

 the foramen ovale, enabling the blood to get to the system without passing through 

 the lungs, by those who regard the arrest of the circulation in asphyxia as due to ob- 

 struction to the pulmonary circulation ; but this explanation is not sufficient, as blood 

 passes easily through the lungs in asphyxia and is obstructed only in the systemic capil- 

 laries. The true explanation seems to be that, in most warm-blooded animals, during the 

 very first periods of extra-uterine life, the demands on the part of the system for oxygen 

 are comparatively slight. At this time, there is very little activity in the processes of 

 nutrition, and the actual consumption of oxygen and exhalation of carbonic acid are 

 much below the usual regular standard in animals of this class. In fact, their condition is 

 somewhat like that of cold-blooded animals. The actual difference in the consumption 

 of oxygen immediately after birth and at the age of a few days is sufficient to explain 

 the remarkable power of resisting asphyxia just after birth. 



One of the most interesting questions, in a practical point of view, connected with 

 the subject of asphyxia, is the effect on the system of air vitiated from breathing in a 

 confined space. There are here several joints which present themselves for considera- 

 tion. The effect of respiration on the air is to take away a certain proportion of oxygen 

 and to add certain principles which are regarded as deleterious. The emanation which is 

 generally regarded as having the most decided influence upon the system is carbonic acid. 

 A careful review of the most reliable observations on this subject shows that the in- 

 fluence of carbonic acid is generally very much over-estimated. In poisoning by char- 

 coal-fumes, it is generally carbonic oxide which is the active principle. Regnault and 

 Reiset exposed dogs and rabbits for many hours to an atmosphere containing twenty- 

 three parts per hundred of carbonic acid artificially introduced, and thirty to forty parts 

 of oxygen, without any ill effects. They took care, however, to keep up a constant sup- 

 ply of oxygen. These experiments are at variance with the results obtained by others, 

 but Regnault and Reiset explain this difference by the supposition that the gases in other 

 observations were probably impure, containing a little chlorine or carbonic oxide. There 

 is no reason to doubt, from the high reputation of these observers for skill and accuracy, 

 that their experiments are perfectly reliable ; and, in that case, they prove that carbonic 

 acid does not act upon the system as a poison. This view is sustained by the observa- 

 tions of Bernard with carbonic oxide, which is known to be excessively poisonous. In 

 animals killed by this gas, the blood, both venous and arterial, is of a bright-red color, 

 which is due to the fixation of the gas by the blood-corpuscles. In this way, the red 

 corpuscles, which act normally as respiratory agents carrying oxygen to the tissues, are 

 paralyzed, and the animal dies from asphyxia. We have already referred to this remark- 

 able affinity of the red corpuscles for carbonic oxide and its action in arresting the trans- 



