regulating Metabolism . 519 
manifestly a phenomenon of supreme importance if it be of general occur- 
rence. It is worth while to inquire whether, for example, the absorption 
of salts by plants may not be in part at least conditioned by such a process ; 
whether the translocation of diffusible matter may not be dependent largely 
upon such a process ? Obviously, the conditions are very different at 
different times of the day ; it is to be supposed that up-grade changes are 
ascendant at one time (whilst light is active) and down-grade changes at 
another : during the latter period it may be well that the tissues are far 
more easily permeable than during the former. The degree of immunity 
under various conditions and at various ages, the occurrence of latent 
diseases at certain seasons, may be largely a question of the resistance 
afforded by septa to penetration — to their liability to become thinned under 
certain conditions. For such reasons, some hesitation may be felt in accept- 
ing all the results that have been obtained with blood corpuscles in ordinary 
glass tubes, for example ; under such conditions they may well have 
properties somewhat different from those they possess in the body. 
