Appetite

Appetite may be defined as a pleasing state of mind based on pleasant past associations with the taste and ingestion of palatable food. It is in the nature of a conditioned reflex. The person with an appetite demand quality in food presented; the individual who is merely hungry is usually satisfied with quantity and eats it stomach is empty and when it undergoes periodic contraction and tonus changes (hunger contractions). When these contractions become very intense coincident hunger pangs are experienced; when the empty stomach stays contracted, hunger becomes continuous rather than periodic. Appetite, on the other hand, is quite independent of gastric filling; e.g., appetite for a tempting dessert at the close of a meal is no less when the gastric capacity is already strained and hunger can no longer be said to exist.

Thirst

This may be defined as a sensation of dryness in the mouth and throat and a craving for liquid. In extreme thirst following prolonged deprivation of water the tongue clings to the roof of the mouth and a lump appears to rise in the throat. The later is probably the sensation evoked when the dry epiglottis or root of the tongue is moved over the pharynx in attempts to swallow. It is a matter of general experience that thirst may be due to local conditions which cause a dryness of prolonged speaking or singing, chewing desiccated foods, or it may be a result of inhibition of salivary flow through feat or anxiety. Thirst frequently occurs after ingestion of an excess of salt and in conditions accompanying, general anhydremia, e.g., after profuse sweating, vomiting, diarrhea, diuresis, hemorrhage, etc.

Tissues of the body

There are five widely distributed basic tissues which are built up, in varying proportions, to form the organs within the body, the body-wall by which they are enclosed and the appendages of the body. They are: - (1) epithelium, (2) connective tissue, (3) sclerous (or skeletal) tissue, (4) muscular tissue, and (5) nervous tissue. Each of these possesses certain distinguishing features and, with the exception of nervous tissue, each is subdivided into a number of varieties, which retain the essential characters of the parent tissue but exhibit specialization of one or more of its constituent elements. The connective and the sclerous (or skeletal) tissues have many morphological features in common and are often grouped together, but they differ very noticeably in their physical properties, for the connective tissues are soft and pliant while the sclerous tissues are hard and rigid

Sclerous tissues

The sclerous (or skeletal) tissues provide the stiffening which is essential for the formation of the general framework of the body. Structurally they are closely allied to the connective tissues, for their constituent cells lie in a matrix in which fibers may, or may not be developed. Physically, however, the sclerous tissues differ from the soft, pliant connective tissues, for the matrix has become solidified.

There are two varieties of sclerous tissue, viz., cartilage, or gristle, and bone. In cartilage the matrix is impregnated with chondrin, which is a mixture of gelatin with muconoid substances. In bone the matrix is impregnated with certain inorganic salts, of which calcium phosphate forms much the greatest proportion.