ules of fat are produced by a transformation of the albuminous contents of the connective-tissue corpuscles. The vesicles are grouped together to form lobules, which in turn form irregular masses supported by connective tissue and blood-vessels.

Retiform Tissue.—This is also a variety of connective tissue made up very largely of white fibers interlacing in all directions. The spaces or areolae are wanting in the usual ground substance, but are filled with fluid. Connective-tissue corpuscles are abundant, but elastic fibers are absent. Adenoid tissue is but ordinary retiform tissue, the spaces of which, however, are filled with lymph corpuscles. It is found in lymphatic glands, in the central nervous system, and other situations.

Fibrous Tissue.-White fibrous tissue is exceedingly abundant and important. It forms the ligaments which hold the bones together, the tendons of the muscles, the membranes covering bones, cartilages, the septa of muscles, etc. Fibrous tissue is tough and strong but wholly inextensible and, in consequence, is admirably adapted to fulfil various mechanical functions in the body. It is quite pliant, bending readily in any direction, but difficult to break. When examined microscopically it is found to be composed of white fibers, resembling in all respects those of areolar tissue. Treated with acetic acid they swell up and become indistinct. When boiled they yield gelatin, a derivative of collagen.

Elastic Tissue.-The elastic tissue is also an important member of the connective-tissue group. It is almost invariably associated with white fibers in some proportion, but in some tissues, as the ligamentum nuchae, the ligamenta subflava, the coats of the large blood-vessels, it exists almost alone. In its pure state it presents a distinctly yellow appearance. The fibers of which it is composed are transparent, but present a distinct outline; they run almost parallel, but give off branches which unite to form a reticulated structure. As the name implies, these fibers are very extensible and elastic. Cartilage and bone have been considered in connection with the skeleton.

Physical and Physiological Properties of Connective Tissue.Among the physical properties may be mentioned consistency, which varies from the semi-liquid to the solid state. This variation depends upon the quantity of water in the individual tissues. Their cohesion, with the exception of the softer varieties, is considerable, and offers great resistance to traction, pressure, torsion, etc. In the various movements of the body, in the contraction of muscles, in supporting weights, in diminishing the effects of shocks, the properties of consistence and cohesion play important parts. Wherever the various forms of connective tissue are found, their chemical

composition and structure are found to be in relation to their mechanical function. If traction be the preponderating force, the structures become fibrous, as in ligaments and tendons, and the cohesion greatest in the longitudinal direction. If pressure be exerted in all directions, as upon membranes, the fibers become interlaced and so offer an uniform resistance. When pressure is exerted in a definite direction, as upon the ends of long bones, the tissue assumes the cartilaginous form. Elasticity is also a property of all connective tissues, but is most marked in those containing an abundance of yellow elastic fibers. Elasticity plays an important rôle in many physiological acts. It not only opposes and limits forces of traction, pressure, torsion, etc., but upon their cessation returns the tissues or structures to their original condition. It thus maintains the natural form and position of the organs by counterbalancing and opposing temporarily acting forces.

CHEMICAL COMPOSITION OF THE HUMAN BODY.

By chemical analysis the solids and fluids of the body can be first reduced to a number of compound substances which are termed proximate principles; these again can be resolved by an ultimate analysis into fifteen chemical elements. The different chemical elements thus obtained, and the proportions in which they exist, are shown in the following table :

Oxygen,

72.00

Hydrogen,

Nitrogen,

9.10
2.50

Carbon,

13.50

Sulphur,

.147

Phosphorus,

1.15

Calcium,
Sodium,

Potassium,

Magnesium, .

:

O. H. and C. are found in all the tissues and fluids of the body, without exception.

O. H. C. and N. found in most of the fluids and all tissues except fat.

In fibrin, casein, albumin, gelatin; as potassium sulpho-cyanide in saliva; as alkaline sulphate in urine and sweat.

In fibrin and albumin; in brain; as tri-sodium phosphate in blood and saliva, etc.

1.30 . . As calcium phosphate in lymph, chyle, blood, saliva, bones, and teeth.

.026

. . As sodium chlorid in all fluids and solids of
the body, except enamel; as sodium sulphate
and phosphate in blood and muscles.
As potassium chlorid in muscles; generally
found with sodium as sulphates and phos-
phates.

.OOI .. Generally in association with calcium, as phos
phate, in bones.

Of the four chief elements which together make up 97 per cent. of the body, O. H. N. are eminently mobile, elastic, and possess great atomic heat. C. H. N. are distinguished for the narrow range and feebleness of their affinities and chemical inertia. C. has the greatest atomic cohesion. O. is noted for the number and intensity of its combinations, and its remarkable display of chemical activity.

Chemical Elements, with the exception of the gases, O. H. and N., do not exist alone in the body, but are combined in characteristic proportions to form compounds, the proximate principles, the ultimate compounds to which the fluids and solids can be reduced.

Proximate Principles exist in the body under their own form, and can be extracted without losing their distinctive properties.

There are about one hundred proximate principles, which are divided into four classes, viz. : inorganic, organic non-nitrogenized, organic nitrogenized, and principles of waste.

Oxygen,

I. INORGANIC PROXIMATE PRINCIPLES.
SUBSTANCE.

Hydrogen,

Nitrogen,

Carbonic anhydrid,
Carburetted hydrogen,

Sulphuretted hydrogen,
Water,

Sodium chlorid,
Potassium chlorid,
Ammonium chlorid,
Calcium chlorid,.
Calcium carbonate, .
Calcium phosphate,
Magnesium phosphate,
Sodium phosphate,
Potassium phosphate,
Sodium sulphate,
Potassium sulphate,

Sodium carbonate,
Potassium carbonate,
Magnesium carbonate,

WHERE FOUND.

Lungs and blood.
Stomach and intestines.
Blood and intestines.

Expired air of lungs.

Lungs and intestines.

Found in all solids and fluids.
In all fluids and solids except enamel.
In muscles, liver, saliva, gastric juice, etc.
Gastric juice, saliva, tears, urine.
Bones, teeth, urine.

Bones, teeth, cartilage, internal ear, blood.

In all fluids and solids of the body.

Universal except milk, bile, and gastric juice.

Bones, blood, lymph, urine, etc.

Blood and sebaceous matter.