592 OF RESPIRATION. 



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 submer- 

 sion 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 immersion, through the influence of fear or other mental emotion, concus- 

 sion 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 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. 



779. It has now been sufficiently proved, both by experiment and by pa- 

 thological observation, that the first effect of the non-arterialization of the 

 blood in the lungs, is the retardation of the fluid in their capillaries ( 738) ; 

 of which the accumulation in the venous system, and the deficient supply to 

 the arterial, are the necessary consequences. It is some time, however, be- 

 fore 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-arte- 

 rialized 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 muscular 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 become enfeebled. The cessation of the heart's contraction is 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 accu- 

 mulation of venous blood ; and on the left to deficiency of the stimulus ne- 

 cessary 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 ven- 

 tricle 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 ( 723, c). 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 artifical respiration : for the replacement 

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

 culation 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. 



780. 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 



