While naturally their power of resistance is greater than that of any other organ, they are nevertheless subject to a number of structural disturbances, other than traumatic, the causes of which are sometimes hereditary, sometimes acquired through deficient properties of the nourishing blood.
Certain tissues which form the connection between the bones and the rest of the organs, and the gradual transition into other tissues, are subjects separate and distinct and will be treated separately.
5. The muscular tissue: As to quantity, the muscular tissue represents the maximum of any in the human body.
The muscles do not only consist solely of this one tissue, but of several others, as do most of the other organs; but here, as in all other cases, the principal component element is called after the organ in which it is chiefly found.
The structure of the muscular tissue varies according to its function, so that we distinguish between the striated and the unstriated or smooth muscles. This, however, has no influence on their chemical composition, a distinctive element of which is muscular fibrin, which has the particular property of contractibility.
6. The mucous membrane tissue: The mucous membrane forms the covering of many of the organs, and its chemical and structural composition is identical in all parts of the body.
It is characterized by a viscid watery secretion from the mucous glands, which are always found in the mucous membrane.
Its extremely delicate nature renders it subject to all sorts of irregularities in chemical composition.
This is the cause of numerous diseases, most of which are due either to overproduction or underproduction of the secretion which regulates numerous functions of the body.
7. The tooth and eye tissue: While very different in external appearance, functions and physical qualities, the teeth and the eyes have nevertheless, the most important part of their chemical composition in common; namely, the fluoric acid, which distinguishes them from all other tissues.