14 



NATURE 



[September 5, 1912 



served locomotor functions and received and trans- 

 mitted from cell to cell stimuli, physical or chemical, 

 received by the organism; while those on the inside, 

 being freed from such functions, tended to specialise 

 in the direction of the inception and digestion of 

 nutrient material ; which, passing from them into the 

 cavity of the invaginated sphere, served for the 

 nourishment of all the cells composing the organism. 

 The further course o-f evolution produced manj' changes 

 of form and ever-increasing complexity of the cavity 

 thus produced by simple invagination. Some of the 

 cell-aggregates settled down to a sedentary life, 

 becoming plant-like in appearance and to some extent 

 in habit. Such organisms, complex in form but simple 

 in structure, are the Sponges. Their several parts are 

 not, as in the higher Metazoa, closely interdependent : 

 the destruction of any one part, however extensive, 

 does not either immediately or ultimately involve death 

 of the rest : all parts function separately, although 

 doubtless mutually benefiting by their conjunction, if 

 only by slow diffusion of nutrient ffuid throughout 

 the mass. There is already some differentiation in 

 these organisms, but the absence of a nervous system 

 prevents any general coordination, and the individual 

 cells are largely independent of one another. 



Our own life, like that of all the higher animals, 

 is an aggregate life ; the life of the whole is the life 

 of the individual cells. The life of some of these cells 

 can be put an end to, the rest may continue to live. 

 This is, in fact, happening every moment of our lives. 

 The cells which cover the surface of our body, which 

 form the scarf-skin and the hairs and nails, are con- 

 stantly dying and the dead cells are rubbed off or 

 cut away, their place being taken by others supplied 

 from living layers beneath. But the death of these 

 cells does not affect the vitality of the body as a whole. 

 They serve merely as a protection, or an ornamental 

 covering, but are otherwise not material to our exist- 

 ence. On the other hand, if a few cells, such as those 

 nerve-cells under the influence of which respiration is 

 carried on, are destroyed or injured, within a minute 

 or two the whole living machine comes to a standstill, 

 so that to the bystander the patient is dead ; even the 

 doctor will pronounce life to be extinct. But this 

 pronouncement is correct only in a special sense. 

 What has happened is that, owing to the cessation of 

 respiration, the supply of oxygen to the tissues is cut 

 oft. And since the manifestations of life cease without 

 this supply, the animal or patient appears to be dead. 

 If, however, within a short period we supply the 

 needed oxygen to the tissues requiring it, all the 

 manifestations of life reappear. 



It is only some cells which lose their vitality at the 

 moment of so-called "general death." Many cells of 

 the body retain their individual life in suitable 

 circumstances long after the rest of the body is dead. 

 Notable among these are muscle-cells. McWilliam 

 showed that the muscle-cells of the blood-vessels give 

 indications of life several days after an animal has 

 been killed. The muscle-cells of the heart in mammals 

 have been revived and caused to beat regularly and 

 strongly many hours after apparent death. In man 

 this result has been obtained by Kuliabko as many as 

 eighteen hours after life had been pronounced extinct ; 

 in animals after days had elapsed. Waller has shown 

 that indications of life can be elicited from various 

 tissues many hours and even days after general death. 

 Sherrington observed the white corpuscles of the blood 

 to be active when kept in a suitable nutrient fluid 

 weeks after remov.d 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 



NO. 2236, VOL. go] 



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 limit 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 the blood-vessels are 

 perfused with an oxygenated solution of salts in cer- 

 tain proportions (Ringer). Such revival and prolonga- 

 tion ol the life of separated organs is an ordinary 

 procedure in laboratories of physiology. Like all the 

 other instances enumerated, 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 ttiey 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 o.xygenated blood to all 

 other cells of the body : without 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 contintied 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 appendi.x or a pharyngeal tonsil ; until that 

 epoch arrives we must relv for their removal on the 

 more rapid methods of surgery 1 



Tlie Maintenance of tlie Life of the Cell-aggregate in 

 the Higher Animals. — Coordinating Mechanisms. 

 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 individual cells. But the life of a cell-aggregate 

 such as composes the bodies of the higher animals is 

 maintained not only by the conditions for the mainten- 

 ance of the life of the individual cell being kept 

 favourable, but also by the coordination of the varied 

 activities of the cells which form the aggregate. 

 Whereas in the lowest Metazoa all cells of the aggre- 

 gate are alike in structure and function and perform 

 and share everything in common, in higher animals 

 (and for that matter in the higher plants also) the 

 cells have become specialised, and each is only adapted 

 for the performance of a particular function. Thus 

 the cells of the gastric glands are onlv adapted for 

 the secretion of gastric juice, the cells of the villi for 

 the absorption of digested matters from the intestine, 

 the cells of the kidney for the removal of waste pro- 

 ducts and superfluous water from the blood, those of 

 the heart for pumping blood through the vessels. 

 Each of these cells has its individual life and performs 



