PRESIDENT’S ADDRESS. 23 
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: 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 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 
tne main’ simple as those for individual cells. But the life of a 
the life of | cell-aggregate such as composes the bodies of the higher 
fe coll. animals is maintained not only by the conditions for the 
te kigher” maintenance of the life of the individual. cell being kept 
eee favourable, but also by the co-ordination of the varied 
niechanisms, 2Ctivities of the cells which form the aggregate. Whereas 
in the lowest Metazoa all cells of the aggregate 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 only 
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 products 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 individual functions. 
But unless there were some sort of co-operation and subordination to 
the needs of the body generally, there would be sometimes too little, 
