20 Correlation of Microseojoic FJiysiology [^SSi, jiuy rff^ 
simple. Is this the case ? * Do we not rather find that highly 
organized suhstances are never produced except as the result of 
two or three processes ? Man cannot assimilate the elements either 
of the earth or air to form living matter. They must first be assimi- 
lated by the plant. The plant nourishes the animal. The animal 
serves as food for a higher grade of animals, or for man. 
According to good authorities, osmose will take place against 
a pressure of several atmospheres. It should be borne in mind 
that this passage of liquids against pressure takes place through 
plaster of Paris, carbonate of lime, and even earthenware, as well 
as through animal and vegetable membranes. 
Eeferring to this point I find the following important passage in 
"Watt's ' Dictionary of Chemistry ' : — 
" In osmose there is a remarkably direct substitution of one of 
the great forces of nature for another force — the conversion, 
namely, of chemical action into mechanical power, t 
" Yiewed in this light, the osmotic injection of fluids may, 
perhaps, supply the deficient link which intervenes between 
chemical decomposition and muscular movement. The ascent of 
the sap in plants appears to depend upon a similar conversion 
of chemical, or, at least, molecular action into mechanical force. 
The juices of plants are constantly permeating the coatings of the 
superficial vessels in the leaves and other organs ; and as these 
evaporate into the air, a fresh portion of the liquid is absorbed by 
the membrane, and evaporates ; and thus a regular upward current 
is established, by which the sap is transferred from the roots to the 
highest parts of the tree. 
" In a similar manner, the evaporation constantly taking place 
from the skin and lungs of animals, causes a continuous flow of the 
animal juices from the interior towards the surface." 
I think we have seen that we do not need to assume the action 
of a special vital force to carry on these all-important changes of 
secretion and excretion in plants and animals. 
Physiologists who agree with Dr. Beale always point to the 
fact that oxygen attacks some tissues of the living body and spares 
others ; but a parallel to this can be found in the behaviour of the 
metal-plates in a voltaic cell, consisting of a plate of zinc and plate 
of copper in dilute acid. So long as they are not united, no action 
takes place. The moment, however, that a connection is established 
between them, the zinc rapidly decomposes the water, with the 
evolution of hydrogen gas. 
The nervous system may possess a controlling power which can 
suspend the action of the respired oxygen, or permit it to take efiect. 
* The answer to the question is, that we really know nothing about it.— 
Ed. M. M. J. 
t Vol. v., 721. 
