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surrounded by a distinctly shadowed ring. These last are frequently 
distinguished by the name of granules. The ultimate molecule had 
never been reached even with the highest magnifying powers. In 
the same manner that the astronomer with his telescope resolves 
nebulae into clusters of stars, and sees other nebulae beyond them, 
so the histologist with his microscope magnifies molecules into 
granules, and sees further molecules come into view. The chemical 
composition of these molecules must vary infinitely, but the author had 
been in the habit of classifying them into three groups and referring 
them to, ls£, the albuminous, 2d, the fatty, and 3 d, the mineral 
compounds. These constituents may be mingled together in vari- 
ous proportions, so as to produce simple and compound molecules. 
In the vast majority of cases they are globular in shape, but they 
may be angular, square, and of various forms. They may differ 
in size or be of tolerably uniform size in the same liquid or sub- 
stance. They may be regularly or irregularly diffused in the matter 
examined. Sometimes they are concentrated in particular places, 
and at others scattered in groups. Their colour is various. Most 
of the pigments in plants and animals are dependent on the forma- 
tion of molecules, which in the human lung have been proved to be 
pure carbon, and in the tissues of plants and animals differently 
tinted kinds of fat or of wax. 
These molecules may be formed in two different ways, — ls£, by 
precipitation in fluids ; 2d, by the disintegration of previously formed 
tissues. The former may be called histogenetic (Jffrog and y'sntug, 
generation), and the latter histolytic ( iffrog and Xvff/g, dissolutio). 
They may be denominated molecules of formation and molecules of 
disintegration. 
Histogenetic molecules are formed either from the union of two 
simple organic fluids or from precipitations occurring in formative 
fluids, holding various substances in solution. Fourteen years ago the 
author read to the Society a paper giving an account of the results 
obtained by a union of oil and liquid albumen, the two organic fluids 
from which molecular matter is most commonly derived. It was 
Dr Ascherson of Berlin, who first discovered the important fact, that 
the mere contact of oil and fluid albumen caused the latter to co- 
agulate in the form of a membrane, which he called the haptogen 
membrane, from ' Awto/au) to come in contact. A more complete 
mixture of two such drops produces, as is well known, a white 
