302 



SCIENCE 



[N. S. YoL. XXXVI. No. 923 



treatment the limit of which can not yet be 

 descried. It is a well-established fact that 

 any part or organ of the body can be main- 

 tained alive for hours isolated from the 

 rest if the blood-vessels are perfused with 

 an oxygenated solution of salts in certain 

 proportions (Ringer). Such revival and 

 prolongation of the life of separated or- 

 gans is an ordinary procedure in labora- 

 tories of physiology. Like all the other in- 

 stances enumerated, it is based on the fact 

 that the individual cells of an organ have 

 a life of their own which is largely inde- 

 pendent, so that they will continue in suit- 

 able 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 specialized in 

 them. This is the case with the nerve-cells 

 of the respiratory center, 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 : without such 

 blood most cells soon cease to live. Hence 

 we examine respiration and heart to de- 

 termine if life is present : when one or both 

 of these are at a standstill we know that 

 life can not be maintained. These are not 

 the only organs necessary for the mainten- 

 ance 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 maintain- 

 ing the life of the rest. On the other hand, 

 the cells composing certain organs have in 

 the course of evolution ceased to be neces- 

 sary, and their continued existence may 



even be harmful. Wiedersheim has enu- 

 merated more than a hundred of these or- 

 gans 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 ar- 

 rives we must rely for their removal on the 

 more rapid methods of surgery! 



We have seen that in the simplest multi- 

 cellular 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 maintenance 

 of the life of the individual cell being kept 

 favorable, but also by the coordination of 

 the varied activities of the cells which form 

 the aggregate. Whereas in the lowest met- 

 azoa all cells of the aggregate are alike in 

 structure and function and perform and 

 share everything in common, in higher ani- 

 mals (and for that matter in the higher 

 plants also) the cells have become special- 

 ized, and each is only adapted for the per- 

 formance of a particular function. Thus 

 the cells of the gastric glands are only 

 adapted for the secretion of gastric juice, 

 the cells of the villi for the absorption of di- 

 gested matters from the intestine, the cells 

 of the kidney for the removal of waste prod- 

 ucts 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 its individ- 

 ual functions. But unless there were some 

 sort of cooperation and subordination to 

 the needs of the body generally, there 

 would be sometimes too little, sometimes too 

 much gastric juice secreted; sometimes too 

 tardy, sometimes too rapid an absorption 

 from the intestine; sometimes too little. 



