410 ON RESPIRATION. 



birth and the employment of resuscitating means, and when probably a much 

 longer time had elapsed from the period of the suspension of the circulation. 



547. It has now been sufficiently proved, both by experiment and by patho- 

 logical observation, that the first effect of the non-arterialization of the blood in 

 the lungs, is the retardation of the fluid in their capillaries ; of which the 

 accumulation in the venous system, and the deficient supply to the arterial, 

 are the necessary consequences. It is some time, however, before a complete 

 stagnation takes place from this cause : since, as long as the proportion of 

 oxygen which remains in the air in the lungs is considerable, and that of the 

 carbonic acid is small, so long will some imperfectly arterialized blood find its 

 way back to the heart, and be transmitted to the system. This blood will 

 have a depressing influence upon the functions of the brain and of the mus- 

 cular system ; which influence is aided by the diminution that gradually takes 

 place in the quantity of blood propelled through the aorta; and the actions of 

 the respiratory muscles and of the heart will therefore soon be enfeebled. . The 

 cessation of the heart's contraction^ due to two distinct causes, acting on the 

 two sides ; for on the right side it is the result of the over-distension of the walls 

 of the ventricle, owing to the accumulation of venous blood; and on the left to 

 deficiency of the stimulus necessary to excite the movement. The property, 

 of contractility is not finally lost nearly as soon as the movements cease; for: 

 the action of the right ventricle may be renewed, for some time after it has 

 ceased, by withdrawing a portion of its contents, either through the pulmo- 

 nary artery, their natural channel, or, more directly, by an opening made in , 

 its own parietes, in the auricle, or in the jugular vein ( 489). On the other 

 hand, the left ventricle may be again set in action, by renewing its appropriate 

 stimulus of arterial blood. Hence, if the stoppage of the circulation have not 

 been of too long continuance, it may be renewed by artificial respiration ; for 

 the replacement by oxygen of the carbonic acid in the air-cells of the lungs, 

 restores the circulation through the pulmonary capillaries ; and thus at the 

 same time relieves the distension of the right ventricle, and conveys to the left 

 the due stimulus to its actions. 



548. Of the mode in which the pulmonary circulation is stagnated by the 

 want of oxygen, and renewed by its ingress into the lungs, no other explana- 

 tion can be given, than that which has been heretofore offered of the capillary 

 circulation in general; namely, that the performance of the normal reaction 

 between the blood and the surrounding medium (whether this be air, water, 

 or solid organized tissue), is a condition necessary to the regular movement of 

 the blood through the extreme vessels.* This view has recently obtained 

 additional support from the experiments of Dr. J. Reid on the Respiration of 

 Azote.t He found that, when the ordinary respiration of an animal is inter- 

 rupted, and the Asphyxia is proceeding to the stage of insensibility, the first 

 effect upon the arterial system is an increased distension (as indicated by the 

 hsemadynamometer), even although the blood is at that time nearly venous 

 in its character ; this indicates that the fluid, now so perverted, is unable to 

 pass with facility through the systemic capillaries, in consequence of its not 

 being in a state fit for the performance of its normal actions. As the stagna- 

 tion in the pulmonary capillaries becomes more complete, however, less and 

 less blood is returned from the lungs to the heart ; and, the systemic arteries 

 being gradually unloaded without being refilled, the pressure of the blood 

 upon their walls diminishes, and at last is no longer experienced. Its dimi- 

 nution is not arrested by causing the animal to breathe nitrogen, although the 

 respiratory movements are renewed, thus proving that the stagnation of the 



* For a fuller discussion of the Pathology of Asphyxia, see the Author's essay on the 

 subject in the Library of Practical Medicine, vol. iii. 

 f Edinb. Med. and Surg. Journal, April, 1841. 



