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TRANSACTIONS OF THE SECTIONS. 99 
same way as solid particles enter into and traverse the substance of the protoplasm 
of an ameeba or other mass of sarcode, 
Whilst-physiologists were engaged in these observations, the late Master of the 
Mint, Mr, Graham, was conducting a series of experiments of the most remarkable 
-kind, and of the utmost importance to physiology, as well as to chemistry and 
physics. He found it necessary to separate two sets of substances as crystalloids and 
colloids,—the colloids being penetrable by the crystalloids as readily as water, the 
erystalloids (such as hydrochloric acid and common salt) passing through organic 
membranes with great freedom, whilst many of the colloids, such as albumen and 
gum, will not penetrate them at all. This discovery has enabled the chemist to 
separate erystalloids from colloids by dialysis, even when they occur in the most 
minute proportions—for instance, to separate 80 or 90 per cent. of a ten-thousandth 
part of arsenious acid in twenty-four hours from porter, milk, or infusions of viscera, 
substances notoriously difficult to analyze. And it has enabled physiologists to ex- 
plain how animal membranes are traversed by various substances which could not 
pass through them without being changed from the colloidal into the crystalloidal 
form. Thus the colloidal starch and albumen of our food scarcely admit of absorp- 
tion until in the process of digestion the starch becomes sugar and the albumen 
albuminose, cagetalloiiel bodies which pass through animal membranes with great 
facility. And again, this crystalloidal albuminose, after having passed into the 
tissues through the membranous walls of the vessels, may become a second time a 
colloid, and be deposited and fixed as tissue-substance, ready in its turn to be per- 
meated by ome lind, either for temporary or more durable purposes in the 
economy, ; 
The affect of this great discovery of Mr. Graham’s shows how impossible is the 
advance of physiology without a corresponding advance in our knowledge of che- 
mistry and physics. 
If basement membranes, the walls of blood-vessels, and of cells are made up of col- 
loidal matter, we can easily understand how they are penetrated by crystalloids ; and 
in like manner it is perfectly possible that they may be traversed by other substances 
in solid forms—as, for instance, the walls of blood-vessels by the corpuscles of the 
blood, No wonder that there is a continual deposition and removal of the consti- 
tuents of the tissues, if so slight a change as that from the crystalloidal to the col- 
loidal form, and the reverse, makes such perfectly marvellous differences in the 
relations of these substances to each other. 
We must look upon the tissues of an animal body as we do upon the substance 
of an amoeba, and recollect how penetrable the surfaces and tissues of animals are ; 
then we shall cease to be startled when we see these parts become the seat 
of entirely new deposits, or find them traversed by migrating blood-corpuscles as 
freely as a colloid is penetrated by a crystalloid. 
It is impossible to foresee what may be the result to physiology of this great 
advance in our knowledge of the varying relations of substances to each other 
according as they present themselves at different times in the opposite physical 
conditions which were described by Mr. Graham as crystalloidal and colloidal. 
But it is plain that we cannot continue to look upon animal membranes as forming 
such decided barriers against the penetration of one tissue by another, or by foreign 
matters, as was once supposed. 
Let me now direct your attention to the present aspect of the question how far 
basement membranes limit the distribution of vessels and nerves and separate them 
from the cells of glands and membranes. 
Mr. Bowman, in his admirable researches into the anatomy of the organs of sense, 
discovered that the filaments of the nerves of smell have a remarkable structure— 
that they are nucleated, finely granular, contain no white substance of Schwann, 
and resemble the gelatinous nerye-fibres. The epithelial surface, too, of the 
olfactory region Mr. Bowman described as differing greatly from that of the 
adjacent parts of the nasal mucous membrane, and as being of a dark sepia tint. 
Subsequent examinations by Hoyer, Max Schultze, and Lockhart Clarke confirmed 
‘these statements; and those of Schultze demonstrated that the cells are of two 
kinds :—one elongated and filled with yellowish granular protoplasm, exposed at the 
outer end of each cell, and containing a clear oval nucleus in clear we in its 
