24 LIFE: ITS NATURE, OKIGIN AND MAINTENANCE 



general death. Sherrington observed the white corpuscles of the blood 

 to be active when kept in a suitable nutrient fluid weeks after removal 

 from the blood-vessels. A French histologist, Jolly, has found that the 

 white corpuscles of the frog, if kept in a cool place and under suitable 

 conditions, show at the end of a year all the ordinary manifestations of 

 life. Carrell and Burrows have observed activity and growth to continue 

 for long periods in the isolated cells of a number of tissues and organs kept 

 under observation in a suitable medium. Carrell has succeeded in 

 substituting entire organs obtained after death from one animal for those 

 of another of the same species, and has thereby opened up a field of 

 surgical treatment, the limits of which cannot yet be descried. It is a well- 

 established fact that any part of the body can be maintained alive for hours 

 isolated from the rest if perfused with serum (Kronecker, frog-heart), or 

 with an oxygenated solution of salts in certain proportions (Ringer). Such 

 revival and prolongation of the life of separated organs is an ordinary pro- 

 cedure in laboratories of physiology. Like all the other instances enume- 

 rated, it is based on the fact that the individual cells of an organ have a 

 life of their own which is largely independent, so that they will continue in 

 suitable circumstances to live, although the rest of the body to which they 

 belonged may be dead. 



But some cells, and the organs which are formed of them, are more 

 necessary to maintain the life of the aggregate than others, on account of 

 the nature of the functions which have become specialised in them. This 

 is the case with the nerve-cells of the respiratory centre, since they 

 preside over the movements which are necessary to effect oxygenation of 

 the blood. It is also true for the cells which compose the heart, since 

 this serves to pump oxygenated blood to all other cells of the body : with- 

 out such blood most cells soon cease to live. Hence we examine 

 respiration and heart to determine if life is present : when one or both of 

 these are at a standstill we know that life cannot be maintained. These 

 are not the only organs necessary for the maintenance of life, but the loss 

 of others can be borne longer, since the functions which they subserve, 

 although useful or even essential to the organism, can be dispensed with 

 for a time. The life of some cells is therefore more, of others less 

 necessary for maintaining the life of the rest. On the other hand, the 

 cells composing certain organs have in the course of evolution ceased to 

 be necessary, and their continued existence may even be harmful. 

 Wiedersheim has enumerated more than a hundred of these organs in the 

 human body. Doubtless Nature is doing her best to get rid of them for 

 us, and our descendants will some day have ceased to possess a vermiform 

 appendix or a pharyngeal tonsil : until that epoch arrives we must rely 

 for their removal on the more rapid methods of surgery ! 



We have seen that in the simplest multicellular organisms, where one 

 cell of the aggregate differs but little from another, the conditions for the 

 maintenance of the life of the whole are nearly as simple as those for 



