APPENDIX — RESPIRATION IN CELLS. 645 



maintenance of life, and it may be destroyed by putting a stop 

 to either one or other of them. 



1. Internal respiration may be completely stopped by pre- 

 venting supplies of fresh blood from reaching the tissues. 

 The stoppage may be general or local. General stoppage of 

 internal respiration is produced by arresting the circulation in 

 the whole body, by stopping the action of the heart, or 

 obstructii g the flow of blood through the large vascular trunks 

 which are connected with it. Internal respiration may be 

 arrested locally in any part of the body by compressing or 

 tying either its arteries or veins. Thus, if the arteries going 

 to the head be tied, so that no fresh blood can reach it, or the 

 veins coming from it be ligatured, so that the deoxygenated 

 blood cannot leave it, the blood which is present in the 

 capillaries of the brain loses all its oxygen and becomes 

 charged with carbonic acid. The nervous centres are thus 

 eftectually suffocated, although the lungs may be working 

 vioorously, and the blood in the rest of the body may be 

 richly arterialised. That the loss of function which follows 

 stoppage of circulation in a part is due to the want of the 

 oxygen carried to it by the blood, rather than to the want of 

 nutriment, is well shown by the experiment of Kronecker, 

 who found that contractility could be restored to the excised 

 gastrocnemius muscle of a frog, after exhaustion by repeated 

 contractions, by passing through its vessels a solution of per- 

 manganate of potash, which supplied oxygen to the interior of 

 the muscle, but conveyed to it no nutrient matter. 



When the circulation is diminished but not completely 

 arrested, as, for example, by weakening the heart, or by 

 contracting without obliterating the lumen of the blood-vessels, 

 or when the oxidising power of the blood is impaired, internal 

 respiration will be diminished, but not stopped. 



The tissues, or at any rate the albuminous tissues, in all 

 probability do not undergo combustion directly, ^.e., the 

 albumen does not combine at once with oxygen. It is first split 

 up by the action of a ferment into (1) nitrogenous substances, 

 which, after being oxidised, form urea, and (2) non-nitrogenous 

 substances, such as fat, and probably also glycogen. When 



