ASPHYXIA. 



261 



Dr. Kay,* which we know to have been care- 

 fully performed, and sufficiently repeated, and 

 which appear to solve satisfactorily all the diffi- 

 culties that have been stated. Bichat had not 

 adverted to the length of time during which the 

 circulation of venous blood by the left side of the 

 heart, is carried on in asphyxia ; but the experi- 

 ments of both Dr. Williams and Dr. Kay prove, 

 that this time is very short, and that before this side 

 of the heart has lost its contractile power, the 

 pulmonary veins have ceased to deliver the blood 

 to it, in such quantity as to maintain any effec- 

 tive action, A short quotation from Dr. Kay's 

 paper will show the evidence for this propo- 

 sition. 



" Experiment 1. The trachea of a large 

 rabbit was tied, the abdomen and chest opened, 

 and at the end of the second minute from the 

 commencement of the experiment, the external 

 iliac artery was divided ; a considerable 

 quantity of dark blood flowed, but at the 

 third minute it had almost ceased to escape. 

 The heart continued contracting vigorously ; 

 very small quantities of dark blood collected 

 slowly every twenty seconds at the extremity 

 of the artery. In five minutes all flow of blood 

 had entirely ceased. The left heart contracted 

 spontaneously for a very considerable period 

 longer. I repeated this experiment with simi- 

 lar results."f Again, one of the variations of 

 the experiment was as follows : " Experiment 3. 

 A rabbit was asphyxiated by tying the trachea. 

 The chest was opened. At the end of three 

 minutes and a half no pulse could be discovered 

 in the aorta. The left auricle was then opened, 

 the blood contained escaped, and for a period 

 of from one to three minutes, blood occasionally 

 collected in very minute quantities, as though 

 it gradually drained from the larger vessels of 

 the lungs, but never, as often as the experiment 

 was repeated, collected in quantity. The heart 

 continued vigorous the usual period." 



" In general," says Dr. Kay, " the pheno- 

 mena of the cessation of motion in the left heart 

 in asphyxia are these. A smaller quantity of 

 blood is received into its cavities, and expelled 

 for a time vigorously into the arteries. The 

 ventricle meanwhile diminishes in size, as the 

 quantity of blood supplied becomes less, until 

 at length, although spontaneous contractions 

 still occur in its fibres, no blood issues from a 

 divided artery, and the ventricle, by contrac- 

 tion, has obliterated its cavity. After this, 

 blood slowly accumulates in the auricle from 

 the large vessels of the lungs ; and its con- 

 tractility continues for a very considerable 

 period."J 



Farther experiments by Dr. Kay show, that 

 after the aorta of an animal has been tied, and 

 after the muscles of its lower extremities have, 

 in consequence, gradually lost all contractile 

 power, that power is restored for a time by the 

 injection of venous blood into the lower portion 

 of the aorta ; and from these, and from some 



' Edinburgh Medical and Surgical Journal, vol. 

 xix. and xxix. 



t Edinburgh Journal, vol. xxix. p. 42. 



$ Ibid, p. 46. 



^ Ibid, p. 53 and 54. 



experiments by Dr. Edwards,* we learn, that 

 the venous blood, though less powerful than 

 arterial in maintaining the vital power of mus- 

 cles, is by no means rapidly destructive to it. 



The changes in asphyxia, in the warm-blooded 

 animals, have, therefore, of late been generally 

 thought to be as follows : that the venous blood, 

 though more or less noxious to all parts of the 

 body which it fully penetrates, is nevertheless 

 transmitted through thelungs in the first instance, 

 in sufficient quantity to stimulate the left side of 

 the heart, and is sent from thence in sufficient 

 quantity to penetrate the brain; that by its 

 action there it destroys the sensibility, but that 

 it passes more and more slowly through the 

 pulmonary vessels, and after a few minutes is 

 no longer delivered to the left side of the heart 

 in such quantity as to keep up regular and 

 efficient contractions there ; and that thus, 

 while the animal life is suddenly extinguished 

 by the noxious influence of venous blood on 

 the brain, the organic life is more gradually 

 brought to a stand by its noxious influence in 

 the lungs, and the consequent failure in the 

 supply of blood to the left side of the heart. 



This explanation is consistent with all the 

 phenomena, and particularly with the very 

 rapid restoration of the flow of blood by the 

 admission of air to the lungs of half-asphyxiated 

 animals, stated by Bichat himself as a difficulty 

 in his view of the subject. 



The more recent experiments by Dr. Kay 

 had, however, led him to question the validity, 

 even of that part of Bichat's doctrine, which 

 has been most generally admitted, viz. the ra- 

 pidly noxious effect of venous blood on the 

 brain and nerves. He found, in various cases, 

 that large quantities of blood from the veins of 

 one rabbit could be injected (slowly and cau- 

 tiously, so as to avoid all injury of the cerebral 

 matter) into the carotid arteries of another, with- 

 out causing more than muscular debility and 

 lassitude ; so that he considers venous blood to 

 be only a weaker stimulus to the brain than 

 arterial, not a direct poison to it; and thinks 

 the sudden insensibility of asphyxia is to be 

 explained by the rapid diminution of the quan- 

 tity, not by the change of quality, of the blood 

 sent to the brain from the heart.f 



And when we bear in mind the fact stated 

 in the outset of this inquiry, that the motion 

 and vivifying power of the nutritious fluid is 

 dependent on its exposure to oxygen, not only 

 in the higher animals, but even in the lowest 

 tribes, and in vegetables, where neither heart 

 nor nervous system exists ; it appears reasonable 

 to suppose, that the chief impediment to the 

 blood's motion, from the failure of the supply of 

 oxygen, will be in the lungs themselves, where the 

 venous blood is accumulated in the greatest quan- 

 tity, and where all the minute vessels carrying it 

 must be most completely exposed to its action, 



But before we can be completely satisfied 

 upon this subject, it will be necessary to carry 

 the inquiry one step further, and to ascertain 

 in what manner the change from venous to 



* De 1'Jnflucnce, &c. p. i. ch.'i. and p. iv. ch. 4' 

 t Treatise on Asphyxia, p. 193 et scq. 



