ing the central nucleus;
E, bird;
F, camel;
G, fish;
H, crab or other invertebrate animal
]

The temperature of the blood varies slightly in different parts of the
circulation. Its average heat near the surface is in health about the
same, _viz_. 98-1/2 degrees F. Blood is alkaline, but outside of the body
it soon becomes neutral, then acid. The chloride of sodium, or common
salt, which the blood contains, gives it a salty taste. In a hemorrhage
from the lungs, the sufferer is quick to notice in the mouth the warm and
saltish taste. The total amount of the blood in the body was formerly
greatly overestimated. It is about 1/13 of the total weight of the body,
and in a person weighing 156 pounds would amount to about 12 pounds.

179. Blood Corpuscles. If we put a drop of blood upon a glass slide,
and place upon it a cover of thin glass, we can flatten it out until the
color almost disappears. If we examine this thin film with a microscope,
we see that the blood is not altogether fluid. We find that the liquid
part, or plasma, is of a light straw color, and has floating in it a
multitude of very minute bodies, called corpuscles. These are of two
kinds, the red and the colorless. The former are much more
numerous, and have been compared somewhat fancifully to countless myriads
of tiny fishes in a swiftly flowing stream.

180. Red Corpuscles. The red corpuscles are circular disks about
1/3200 of an inch in diameter, and double concave in shape. They tend to
adhere in long rolls like piles of coins. They are soft, flexible, and
elastic, readily squeezing through openings and passages narrower than
their own diameter, then at once resuming their own shape.

The red corpuscles are so very small, that rather more than ten millions
of them will lie on a surface one inch square. Their number is so enormous
that, if all the red corpuscles in a healthy person could be arranged in a
continuous line, it is estimated that they would reach four times around
the earth! The principal constituent of these corpuscles, next to water,
and that which gives them color is _haemoglobin_, a compound containing
iron. As all the tissues are constantly absorbing oxygen, and giving off
carbon dioxid, a very important office of the red corpuscles is to carry
oxygen to all parts of the body.

181. Colorless Corpuscles. The colorless corpuscles are larger
than the red, their average diameter being about 1/2500 of an inch. While
the red co