" Leaving aside its color, we all know that blood is thicker than water; this is true not only in a metaphorical but in a literal sense. In the first place, bulk for bulk, blood is heavier than water; ten teaspoonfuls of blood weigh as much as ten and a half tea-spoonfuls of water. Secondly, blood contains in it solid corpuscles and when drawn from the body forms spontaneously a solid clot, while pure water has no solid bodies floating in it, and can only be made solid by freezing. Thirdly, the blood liquid itself, quite apart from the corpuscles, is thicker than pure water, because it contains a great many things dissolved in it; things which are of great importance, because they are the foods which the blood is carrying to, and the wastes which it is carrying from, the various organs of the body".

The Composition Of Blood Serum

About one half of the bulk of fresh blood is corpuscles and the other half plasma. What the plasma contains we may learn by examining blood-serum, which is plasma minus fibrinogen.

When does blood clot? Illustrate the uses of the coagulating property of blood.

Compare blood with water, (1) as to the weight of equal bulks of the two (specific gravity); (2) as to its microscopic structure; (3) as to its tendency to solidify; (4) as to the composition of its plasma. Why are the things dissolved in the plasma of great importance?

What is the relative proportion of corpuscles and plasma in blood?

Blood-serum is very different from water; if we keep on boiling pure water in a saucepan it will all go off in steam and leave nothing behind, but if we try to boil serum we find that we cannot do it; before it gets as hot as boiling water it sets into a stiff, solid mass just like the white of a hard-boiled egg. In fact the serum contains dissolved in it two albumens very like that in the white of an egg, and coagulated in a similar way by boiling. About eight and a half pounds of albuminous substances exist in one hundred pounds of blood.

Blood-serum also contains considerable quantities of oily and fatty matters, a little sugar, some common salt and carbonate of soda, and small quantities of very many other things, chiefly waste products from the various tissues. Nine tenths of the blood-plasma is water.

Composition Of The Bed Corpuscles

In the fresh moist state these contain a little more than half their weight of water. Nine-tenths of their solid part is Hæmoglobin ; they also contain phosphorus and iron and potassium.