514 PROFESSOR S1MONDS* LECTURE. 
veins the returning conduits. In vertebrated animals this fluid 
was of a red colour, but in the invertebrated it was colourless. 
While circulating it appeared to be a red homogeneous fluid; but 
upon being drawn it separated into solid and fluid portions, and, if 
analysed, it would be found to be made of dissimilar parts. It con¬ 
tained, in reality, four chief components—fibrin, albumen or serum, 
corpuscles, and salts, each of which had an important part to play 
in the system. The redness of the blood was found to depend 
altogether upon the presence of the red particles; remove these, and 
it would become colourless. Blood, when drawn from an animal, 
coagulated, and this coagulation depended upon the presence of 
the material called fibrin, and by the amount of this they could 
ascertain its nutritive quality. After the blood had stood for some 
time, a fluid appeared on its surface of a pale yellow colour, the 
serum, which possessed no power in itself to coagulate, and had a 
specific gravity a little above that of water. Serum, although in 
reality a fluid, contained an important element, which was capable 
of undergoing solidification, but not spontaneously. This was al¬ 
bumen, which it was well known solidified by heat; and if he were 
to expose some serum to a heat of 160 degrees it would coagulate. 
It would also coagulate by an admixture with the mineral acids. 
[The Lecturer illustrated this by mixing some acid with a quantity 
of serum in a glass jar.] 
He next proceeded to notice the constituents and qualities of 
fibrin, which 'vas obtained from the bloo 1 before it coagulated. 
It might justly be described as the basis of the animal machine. 
It formed plugs in cases of haemorrhage, and temporary bonds in 
fractures. It was self-coagulating, white in texture, tough and 
elastic. It was found to exist in a larger relative quantity in 
arterial than in venous blood, because the arteries appropriated a 
quantity prior to the passage of the blood into the veins, thus 
shewing how important fibrin was to the support of the system. 
He then spoke of the red particles found in the blood, and which 
gave colour to the fluid. There were thousands of these bodies in 
a drop of blood ; but they were so minute that they could not be 
discovered without the aid of the microscope. It was formerly 
supposed that there were certain parts of the body the blood in 
which did not contain them, and that the eye was one of those 
parts; but modern research had disproved this position. It had 
been found that the blood in the eye was supplied with these par¬ 
ticles, but not in sufficient quantity to colour it. The microscope, 
as before stated, was necessary to develop their existence, and 
when thus examined they were found to be flattened discs, varying 
in size from the 4500th to the 2800th part of an inch. They might 
take the general average size at the 3000th part of an inch. These 
