EFFECTS OF RESPIRATION ON THE BLOOD. 409 



water being removed, and a- considerable addition being made to the amount 

 of oxygen which it contains : its arterial hue and character are thus restored. 

 It may be observed, then, that the blood, by its alternate passage through the 

 systemic and pulmonary capillaries, serves to bring the two into close rela- 

 tion ; and that in this manner, the oxygen of the air is enabled to act upon the 

 minutest portions of those tissues of the body that are most distant from the 

 lungs, as completely as it can do by being directly introduced into their sub- 

 stance, as it is in Insects. It is interesting to remark that these are the only 

 Invertebrata in which there is an active respiration ; and it would seem as if 

 the universal permeation of their tissues by tracheae is a compensating struc- 

 ture, making up for that deficiency in the carrying power of the blood, which 

 may be attributed to the absence of red corpuscles ( 576). 



546. We have now to consider the results of the cessation of the Respiratory 

 function, and the consequent retention of carbonic acid in the blood. If this 

 be sufficiently prolonged, a condition ensues to which the name of Asphyxia 

 has been given ; the essential character of which is the cessation of muscular 

 movement, and shortly afterwards of the circulation ; with an accumulation of 

 blood in the venous system. The time which is necessary for life to be de- 

 stroyed by asphyxia varies much, not only in different animals, but in different 

 states of the same. Thus, Warm-blooded animals are much sooner asphyxiated 

 than Reptiles or Invertebrata; on the other hand, a hybernating Mammal 

 supports life for many months, with a respiration sufficiently low to produce 

 speedy asphyxia if it were in a state of activity. And among Mammalia and 

 Birds, there are many species which are adapted, by peculiarities of conforma- 

 tion, to sustain a deprivation of air for much more than the average period.* 

 Excluding these, it may be stated as a general fact, that, if a warm-blooded 

 animal, in a state of activity, be deprived of respiratory power, its muscular 

 movements (with the exception of the contraction of the heart) will cease 

 within five minutes, often within three ; and that the circulation generally 

 fails within ten minutes. Many persons, however, are capable of sustaining 

 a deprivation of air for three, four, or even five minutes, without insensibility 

 or any other injury ; but this power, which seems possessed to the greatest 

 degree by the divers of Ceylon, can only be acquired by habit. The period 

 during which remedial means may be successful in restoring the activity of 

 the vital and animal functions, is not, however, restricted to this. Cases are 

 not unfrequent, of the revival of drowned persons after a submersion of half 

 an hour; and more than one has been credibly recorded, in which above 

 three-quarters of an hour had elapsed. It is not improbable, however, that in 

 some of these cases a state of Syncope had come on at the moment of immer- 

 sion, through the influence of fear or other mental emotion, concussion of the 

 brain, &c, ; so that, when the circulation was thus enfeebled, the deprivation 

 of air would not have the same injurious effect as when this function was in 

 full activity. The case would then closely resemble that of a hybernating 

 animal ; for in both instances the being might be said to live very slowly, and 

 would therefore not require the usual amount of vital stimuli. The condition 

 of the still-born infant is in some respects the same ; and re-animation has been 

 successfully attempted, when nearly half an hour had intervened between 



* Thus, the Cetacea contain far more blood in their vessels than do any other Mamma- 

 lia; and these vessels are so arranged, that both arteries and veins are in connection 

 with large reservoirs or diverticula. The reservoirs belonging to the former are usually 

 full; but when the Whale remains long under water, the blood which they contain is 

 gradually introdiBed into the circulation, and, after becoming venous, accumulates i 

 the reservoirs connected with the venous system. By means of this provision, the Whale 

 can remain under water for more than an hour. 

 35 



