632 NERVOUS SYSTEM. 



in connection with the physiology of respiration. Under normal condi- 

 tions, the centres on the two sides probably operate through the pneurnogas- 

 tric nerves and the respiratory movements on the two sides are synchronous. 

 That there is a respiratory centre on either side, is shown by the experiment 

 of dividing the medulla longitudinally in the median line, the respiratory 

 movements afterward continuing with regularity. If, now, the pneumogas- 

 tric be divided on one side, the respiratory movements on that side become 

 slower and are no longer synchronous with the movements on the opposite 

 side. This shows that while the respiratory centres on the two sides nor- 

 mally act together, being undoubtedly connected with each other by com- 

 missural fibres, each one has independent connections with the pneumo- 

 gastric on the corresponding side of the body. 



Cardiac Centres. There can be scarcely any doubt with regard to the 

 existence of cardiac centres in the medulla perhaps an inhibitory centre 

 and an acceleratory centre but the situation of these centres has not been 

 exactly determined. The influence of the nerves and nerve-centres over the 

 movements of the heart has been fully considered in connection with the 

 physiology of the circulation. 



Vital Point (so called). Since it has been definitely ascertained that 

 destruction of a restricted portion of the gray substance of the medulla 

 produces instantaneous and permanent arrest of the respiratory movements, 

 Flourens and others have called this centre the vital knot, destruction of 

 which is immediately followed by death. With the existing knowledge of the 

 properties and uses of the different tissues and organs of which the body is 

 composed, it is almost unnecessary to present any arguments to show the un- 

 philosophical character of such a proposition. One can hardly imagine such 

 a thing as instantaneous death of the entire organism ; and still less can it be 

 assumed fhat any restricted portion of the nervous system is the one, essential 

 vital point. Probably, a very powerful electric discharge passed through the 

 entire cerebro-spinal axis produces the nearest approach to instantaneous 

 death ; but even then it is by no means certain that some parts do not for a 

 time retain their physiological properties. In apparent death, the nerves 

 and the heart may be shown to retain their characteristic properties ; the 

 muscles will contract under stimulus, and will appropriate oxygen and give 

 oil carbon dioxide, or respire ; the glands may be made to secrete, etc. ; and 

 no one can assume that under these conditions, the entire organism is dead. 

 There seems to be no such thing as death, except as the various tissues and 

 organs which go to make up the entire body become so altered as to lose 

 their physiological properties beyond the possibility of restoration ; and this 

 never occurs for all parts of the organism in an instant. A person drowned 

 may be to all appearances dead, and would certainly die without measures 

 for restoration ; yet in such instances, restoration may be accomplished, the 

 period of apparent death being simply a blank, as far as the recollection of 

 the individual is concerned. It is as utterly impossible to determine the ex- 

 act instant when the vital principle, or whatever it may be called, leaves the 

 body in death, as to indicate the time when the organism becomes a living 



