228 RESPIRATION. 



ments, or permitting them to continue in an atmosphere 

 deprived of uncombined oxygen, the circulation of blood 

 through the lungs is retarded, and at length stopped. The 

 immediate effect of such retarded circulation is an obstruc- 

 tion to the exit of blood from the right ventricle : this is 

 followed by delay in the re'turn of venous blood to the heart ; 

 and to this succeeds venous congestion of the nervous centres 

 and all the other organs of the body. In such retardation, 

 also, an unusually small supply of blood is transmitted 

 through the lungs to the left side of the heart ; and this 

 small quantity is venous. 



The condition, then, in which a suffocated, or asphyxi- 

 ated animal dies is, commonly, that the left side of the 

 heart is nearly empty, while the lungs, right side of the 

 heart, and other organs, are gorged with venous blood. 

 To this condition many things contribute. 1st. The ob- 

 structed passage of blood through the lungs, which appears 

 to be the first of the events leading to suffocation, seems 

 to depend on the cessation of the interchange of gases, as 

 if blood charged with carbonic acid could not pass freely 

 through the pulmonary capillaries. But the stagnation of 

 blood in the pulmonary capillaries would not, perhaps, be 

 enough to stop entirely the circulation, unless the action 

 of the heart were also weakened. Therefore, 2ndly, the 

 fatal result is probably due, in some measure, to the 

 enfeebled action of the right side of the heart, in conse- 

 quence of its over -distension by blood continually flowing 

 into it ; this flow, probably, being much increased by the 

 powerful but fruitless efforts continually made at inspira- 

 tion (Eccles). And ^rdly, because of the obstruction at the 

 right side of the heart, there must be venous congestion in 

 the medulla oblongata and nervous centres : and this evil 

 is augmented by the left ventricle receiving and propelling 

 none but venous blood. Hence, slowness and disorder of the 

 respiratory movements and of the movements of the heart 

 may be added. Under all these conditions combined, the 



