TRIPOD OF LIFE. 377 



more of renewed circulation siifFice to restore them to their 

 normal state. It might almost seem that the tripod of life had 

 been reduced to one leg — viz., a circulating apparatus or heart ; 

 but this is not the case, for it must be remembered that the 

 blood which circulates must be oxygenated or arterial ; and if, 

 as in the case of artificial circulation, there be no lungs to effect 

 its oxygenation, their place must be supplied by agitation with 

 air, though this is at best but a poor substitute. Indeed, it is 

 rather because the blood carries oxygen than nutriment to the 

 tissues that arrest of circulation causes them to die so speedily ; 

 for Kronecker found* that, after he had exhausted the muscles 

 of a frog by constant irritation, he could restore their contrac- 

 tility by passing through their vessels a solution of permanganate 

 of potash, which, like the blood, could supply them with oxygen, 

 although it could yield them no nourishment. 



The body is made np of a number of parts ; and if the heart 

 stop, the circulation ceases ; or, if the lungs fail to perform 

 their duty, so that the circulating blood is no longer arterial- 

 ised, all the parts, and therefore the whole body, will die. But 

 the parts will not all die at the same time ; and this is a point 

 of great practical importance. The brain and spinal cord 

 generally die first, and the heart may be pulsating as regularly 

 as ever when all respiratory movements have ceased, and no 

 irritation, however intense, will evoke the faintest indication 

 of consciousness, or excite the slightest reflex action. The 

 muscles retain their irritability still longer than the heart, and 

 they continue to possess their power of contraction, and the 

 lungs their ability to oxygenate the blood, even after the cardiac 

 pulsations have entirely ceased. Here, then, we come to the 

 third leg of the tripod of life — viz., the brain — for want of which 

 the other two cannot stand. The whole body, in fact, may be, 

 and often is, alive, with the exception of the nervous centres. 

 The heart is alive, the lungs are alive, but the brain is dead, 

 and, without it, the respiratory muscles will not work. The 

 want of oxygen weakens the heart ; it gradually stops, and then 

 the other parts of the body die, each in its turn. But, if the 

 respiration can only be kept up artificially, the heart will go on 



* Ludwig's Arheiten, 1872, p. 182. 



