262 



ASPHYXIA. 



arterial blood so greatly promotes the flow of 

 blood through the capillaries of the lungs, and 

 how the presence of venous blood in the begin- 

 nings of the pulmonary veins can so effectually 

 retard it, that the action of the right ventricle of 

 the heart, though continuing vigorous for a 

 time thereafter, fails of its wonted effect, and the 

 blood stagnates in those capillaries. 



The common expression employed on this 

 subject is, that arterial blood is a stimulus 

 peculiarly adapted to excite the capillaries of 

 the lungs and pulmonary veins ; and that 

 venous blood stagnates in those capillaries for 

 want of power to excite them. But it must 

 be remembered that we have no distinct evi- 

 dence of the existence of coats, still less of 

 irritable coats in the minute capillaries of the 

 lungs ;* that although the circulation there has 

 been often examined with the microscope, no 

 contraction of the vessels has ever been ob- 

 served ; that the only vital power of contrac- 

 tion which experiments authorize us to ascribe to 

 any arteries, is a power of permanent or tonic 

 contraction on their contents, which, when 

 called into action, lasts for some time, and 

 while it lasts must obviously impede the flow 

 of fluids through these vessels ; that on these 

 grounds Magendie and other eminent physio- 

 logists believe the only power, which arteries 

 can exercise over their contents, to be simply a 

 power of either relaxing, so as to give them a free 

 passage, or contracting so as to lessen and re- 

 tard their flow ;f and that, conformably with 

 these views, it was found by Wedemeyer, that 

 when he injected stimulating liquids into the 

 arteries of living animals, they were much 

 longer of making their way into the veins, than 

 mild liquids were.J 



These considerations evidently point to the 

 conclusion, that, if the difference depend on any 

 vital action of vessels, venousblood,\vhich makes 

 its way so slowly through the capillaries of the 

 lungs, must be the stronger stimulus to them, and 

 that arterial blood, which is transmitted so readily, 

 must act as a sedative, to the only vital action 

 of which these vessels are susceptible. But 

 this conclusion is again strongly opposed by 

 the fact, that in all other instances, in relation 

 to muscular contraction, to the functions of 

 the nervous system, and of secreting organs, 

 arterial blood, and the oxygenated fluids in 

 general, manifestly possess the stimulating 

 power, and venous blood or carbonized fluids 

 the sedative. 



In this difficulty it is important to remember, 

 that we have many facts to indicate the exist- 

 ence of powers which move the blood and 

 other organized fluids in living animals, inde- 

 pendently of any contractions of moving solids. 

 It would appear that the power by which any 

 texture is nourished, or secretion or excretion is 

 formed from the blood, in any part of the circu- 

 lation, is, to a certain degree, a cause of move- 

 ment of the blood towards that part,and that any 

 stimulus given to such act of nutrition or secre- 



* See Marshall Hall on the Circulation, p. 47. 



t Physiology, translated hy Milligan, p. 409-10. 

 Mayo's Outlines, (2nd edit.) p. 87 et seq. 



* Edinburgh Medical Journal, July 1829, p. 90. 



tion, although applied at the extremity of the 

 capillaries, produces an effect on the circulation 

 which, as Sir C. Bell expresses it, is retrograde 

 along the branches of the arteries. Thus, the flow 

 of blood to the mucous membrane of the stomach 

 and bowelsduring digestion, to the uterus during 

 gestation, to the mammae during lactation, to 

 any part of the body during inflammation, sup- 

 puration, or the growth of a tumour, is excited 

 by causes acting at the extremities of the arte- 

 ries of these parts ; although there is the same 

 difficulty in all these cases, as in the case of the 

 lungs, in understanding how a cause acting 

 there, and exciting the only vital power which 

 arteries can be shewn to possess, should in- 

 crease the flow of blood through them. 



It is always to be remembered, that pre- 

 cisely analogous phenomena are observed from 

 the application of heat, or other stimuli, to 

 single branches, or roots, of vegetables, where 

 there is no evidence of the existence, either 

 of a structure or of a contractile power, m 

 the vessels or cells through which the fluids 

 pass, capable of giving them a determinate 

 direction towards the parts, which are thus 

 stimulated; and where the movement of fluids 

 that can be seen, (in the case of those plants 

 that have milky juices,) is not only unattended 

 with any visible contraction of solids, but is 

 of a kind, (as the recent observations of 

 Schultze, Amici, Raspail, and otheis indicate,) 

 which no contractions of solids appear capa- 

 ble of producing. 



It is farther to be observed, that when venous 

 blood becomes arterial, it acquires an increase 

 of fibrin,* and that its tendency to coagulation 

 is decidedly increased,t which implies such an 

 increase of an attraction of aggregation in the 

 particles of the fibrin, as may be held to 

 be strictly vital. And on the other hand, 

 when arterial blood becomes venous, according 

 to the microscopical observations of Kalten- 

 brunner, its globules seem to separate some- 

 what from one another, and its whole bulk ap- 

 pears somewhat increased. J 



Lastly, it is to be remembered, that when a 

 vessel is opened in a living animal, and the 

 blood exposed to the air, the consequence is, 

 a movement of derivation of the blood, in all 

 directions, towards the aperture ; which is cer- 

 tainly altogether independent of the heart's 

 action, and which the elaborate investigations 

 of Haller led him (and apparently with good 

 reason) to think inexplicable likewise by any 

 contraction of vessels. 



The consideration of all these facts may 

 lead us strongly to suspect, that the stimulus 

 to the circulation which is given by the arte- 

 rialization of the blood, and which we have 

 found to act chiefly in the capillaries of the 

 lungs, is of the nature of an attraction of the 

 venous blood towards the part where it is to 



* Prevost and Dumas, An. de Chimie, t. xxiii. 



t See particularly Schroeder Van der Kolk, Com. 

 de Sanguine Coagulante. 



t Experimcnta circa Statum Sanguinis, &c. 281 

 &357. 



Mem. sur le Mouvement du Sang, p. 336 et 

 seq. 



