ASPHYXIA. 491 



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 obstruction to the pulmonary circulation ; but this expla- 

 nation is not sufficient, as blood passes easily through the 

 lungs in asphyxia, and is obstructed only in the systemic 

 capillaries. 



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 light. 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 very much below 

 the 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. 

 The comparative observations of Edwards on dogs, cats, and 

 Guinea pigs, show, that this power bears a definite relation 

 to the respiratory activity. 



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 points presented for consideration. 

 The effect of respiration on the air is to take away a certain 

 proportion of oxygen, and 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 influence of carbonic acid is generally 

 very much over-estimated. In poisoning by charcoal fumes, 

 it is generally carbonic oxide which is the active princi- 



