118 SECTIONAL ADDRESSES. 
higher animals, the organism as a whole becomes, under conditions of our 
present imperfect control, irrevocably older, and each cycle of rest brings 
with it less rise in metabolic rate. In the lower animals and in hibernating 
members of the higher forms, extensive rejuvenescence takes place. The 
senile effect is indefinitely postponed. Physiological isolation of a part 
occurs from various causes—increased growth and relatively decreased 
subordination to dominance, position off the line or beyond the main force 
of the gradient. Such isolated regions re-acquire the higher rate of meta- 
bolic change, and establish a new gradient system or a renewed system 
based in either case on local differences in rate of stimulus. Such physio- 
logically isolated pieces we call germ-cells, buds or spores, but there appears 
to be complete gradation between the rhythm or cycle of rest and activity 
in the functional units of an organ, and the periodic ripening, discharge and 
activation of ova or the periodic production of medusaeand of resting stages 
of Polyzoa or Sponges. To use Professor James Johnstone’s phrase, the 
tendency of the universe to run down, or of entropy to increase, is opposed 
by phases in the cycles of life. The alternation of the physiologically 
younger state with the more highly differentiated older state is fundamental. 
Periodicity in Organic Function. 
Intimately connected with the idea of the organism as a synthesis of 
co-ordinated control is the principle of periodicity in the functioning of 
organs. This is a development of an old idea and is widely recognised by 
physiologists and pathologists. It may be expressed in the phrase that 
at any time the organism or any part of it, is a function of its own cyclical 
period, or, as I have just expressed it, an animal works its organs in shifts. 
What the shift-unit may be for each organ we do not know; we do know 
that, for the higher animals, more tissue exists than is needed for well-being 
under average circumstances, and that when a time of special stress ensues 
the emergency is met, not so much by increasing the pressure on the work- 
ing shift, as by calling up the reserves and throwing them into the general 
action. 
The evidence for ‘ partial activity,’ as the pathologists call this economic 
exercise of function, is partly direct, by tests indicative of activity or 
repose, and partly by the results of observation on the removal of organs 
or parts of organs. The glomeruli of the mammalian (rabbit) kidney 
have, by suitable means, beenmade to showtheir fields of activity at a given 
moment, and the result shows patches of active glomeruli alternating 
with inactive ones. Again, removal of a large portion of the liver is not 
necessarily fatal to man, nor is it essential that both kidneys should be 
present. Removal of one of the kidneys and a study of the after-effects 
confirms the conclusion that one kidney can do the work of both, and that 
a much smaller liver than is normally present can sustain the body in 
health. Similar conclusions apply to other tissues, and there is great need 
for the extension of research on these lines to the partial activity of animals. 
Two considerations of great practical importance for our present study 
of control as a principle of organisation arise out of an analysis of this 
view of cyclical functioning of parts of an organ. The first is that the rest- 
ing{shift is receiving less blood and is more resistant to disease than when 
it is working. It is in a state of less active metabolism,'and while recovering 
