EFFECTS OF SUSPENSION OR DEFICENCY OF RESPIRATION. 537 



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 accu- 

 mulation 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 exerts a depressing influ- 

 ence upon the nervous centres, which is aided by the diminution that gradually 

 takes place in the quantity of blood propelled to them ; and thus the powers of the 

 Sensorial centres are suspended, so that the individual becomes unconscious of 

 external impressions ; whilst the activity of the Medulla Oblongata also becomes 

 diminished, so that the respiratory movements are enfeebled. The progressive 

 exhaustion of the oxygen of the air in the lungs and the accumulation of carbonic 

 acid in the blood, increase the obstruction in the pulmonary capillaries ; less 

 and less blood is delivered to the systemic arteries, and what is thus transmitted 

 becomes more and more venous -, the nervous centres are now completely pa- 

 ralyzed, and the respiratory movements cease ; and the deficient supply of blood, 

 with the depravation of its quality, act injuriously upon the muscular system 

 also, and especially weaken the contractility of the heart ( 324). In this en- 

 feebled state, the final cessation of its movements seems attributable to two dis- 

 tinct causes, acting on the two sides respectively ; for on the right side is the 

 result of the over-distension of the walls of the ventricle, owing to the accumu- 

 lation of venous blood ; and on the left to deficiency of the stimulus necessary 

 to excite the movement, which is no longer sustained by its spontaneous motil- 

 ity ( 499). The heart's contractility is not finally lost, nearly as soon as its 

 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 pulmonary artery, their natural channel or, more directly, by an opening 

 made in its own parietes, in the auricle, or in the jugular vein ( 504). 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 circula- 

 tion have not been of too long continuance, it may be renewed by artificial re- 

 spiration ; for the replacement of the carbonic acid by oxygen 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. Of the mode in which the Pulmo- 

 nary circulation is thus stagnated by the want of oxygen, and renewed by its 

 ingress into the lungs, no other consistent explanation can be given, than that 

 which is based on the doctrine already laid ddwn in regard to the capillary circu- 

 lation in general ( 527) ; 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. That no mechanical impediment to its 

 passage is created (as some have maintained) by the want of distension of the 

 lungs, has been fully proved by the experiments of Dr. J. Reid on the induction 

 of Asphyxia by the respiration of azote. And that a contraction of the small 

 arteries and capillaries, under the stimulus of venous blood, cannot be legiti- 

 mately assigned as the cause of the obstruction, is evident from the consideration 

 brought to bear upon it by the same excellent experimenter ( 526) ; namely, 

 the suddenness with which the flow is renewed on the admission of oxygen, as 

 contrasted with the slowness with which arteries dilate after the removal of the 

 cause of their contraction. 1 



1 For a fuller discussion of the Pathology of Asphyxia, see the " Cyclop, of Anat. and 

 Phys.," art. "Asphyxia," by Prof. Alison; the "Library of Practical Medicine," vol. iii. 



