tissues, which have been suitably prepared and mounted for microscopic
study, using low and high powers of the microscope. Make drawings of the
cells in the different tissues thus observed.




CHAPTER IV - THE BLOOD


Two liquids of similar nature are found in the body, known as the blood
and the lymph. These are closely related in function and together they
form the nutrient fluid referred to in the preceding chapter. The blood is
the more familiar of the two liquids, and the one which can best be
considered at this time.

*The Blood: where Found.*—The blood occupies and moves through a system of
closed tubes, known as the blood vessels. By means of these vessels the
blood is made to circulate through all parts of the body, but from them it
does not escape under normal conditions. Though provisions exist whereby
liquid materials may both enter and leave the blood stream, it is only
when the blood vessels are cut or broken that the blood, as blood, is able
to escape from its inclosures.

*Physical Properties of the Blood.*—Experiments such as those described at
the close of this chapter reveal the more important physical properties of
the blood. It may be shown to be heavier and denser than water; to have a
faint odor and a slightly salty taste; to have a bright red color when it
contains oxygen and a dark red color when oxygen is absent; and to
undergo, when exposed to certain conditions, a change called coagulation.