A considerable number of different tissues go to the make-up of the body, but they can all be included in four groups, namely, nervous tissue, muscular tissue, epithelial tissue and connective tissue. Essentially, any tissue consists of cells and an intercellular substance, though the characters and the relative proportions of each of these may vary. Thus, epithelium consists almost entirely of cells with very little intercellular substance, while in some kinds of connective tissue the opposite is found.
A cell consists of a mass of protoplasm containing a nucleus. The protoplasm is composed of a more solid element in the form of a network, known as the spongioplasm, in the interstices of which is a more liquid part, the hyaloplasm. The nucleus is surrounded by a membrane and its substance also consists of a spongy part, the nuclear reticulum, and a more liquid part, the nuclear lymph. Within the nucleus there is contained a tiny rounded body known as the nucleolus; sometimes there is more than one. The membrane, the reticulum, and the nucleolus contain a substance which takes on certain stains; thus called chromatin.
Cells multiply by dividing and occasionally the division is a simple process, but almost always it is a complicated process called karyokinesis. Here there is first a definite rearrangement of the chromatin filaments and then a division through these.
There are several varieties of connective tissue, including jelly-like tissue, fibrous tissue, cartilage, bone and blood. In these the cells and the intercellular tissue differ in character. In blood the latter is constituted by the plasma. In the jelly-like tissue, which occurs in the umbilical cord and forms the vitreous humor of the eye, a clear, soft substance forms the great bulk of the tissue, while in fibrous tissue most of the bulk consists of white fibers which have been laid down in a homogeneous matrix, or ground substance.
How bone and cartilage are formed:
Cartilage, or gristle, consists of a ground substance in which numerous cells and sometimes fibers, white or yellow elastic, are disposed. Cartilage containing fibers is called fibrocartilage, white fibrocartilage or yellow elastic fibrocartilage as the case may be. Cartilage with a clear matrix is called hyaline cartilage.
That there is some connection between the thymus and the sex glands, as removal of the testes delays the disappearance of the thymus, and removal of the thymus, on the other hand, causes precocious development of the testes. Moreover, there may be some connection with general development, as in some instances of poor bodily development and muscular weakness, the thymus has been found to be prematurely atrophied. An overgrowth of the thymus occurs in what is called the status lymphaticus, and also in some other disorders.
Such over-growth may easily be dangerous owing to pressure on the windpipe, and such pressure is the cause of thymic asthma, this being the name given to urgent attacks of difficulty in breathing which occur in infants and sometimes cause sudden death. The only treatment for this condition is removal of the thymus, but this is a difficult operation. In rare instances the thymus is the seat of cancer.
Application and treatment:
A gland is an organ that produces a specific secretion. Polarize positive in the area of the thymus. Always use extreme caution when treating children, especially infants.