4G3 



(4) In cartilar/e a mass of firm amorphous substance, witli no vas* 

 ciilarity and little vitality, forms the bed for the choudroplasts or cells 

 of this tissue. 



(5) Bone differs from the above iu having the amorphous matter im- 

 preguated with lime salts, which gives it its rigidity and firmness. 



(G) Epitlielia and endotJielia, or the membranes which cover the body 

 and line all of its cavities and glands, are made up of single or strati- 

 fied and multiple layers of cells bound together by a glue of amorphous 

 substance, and resting on a layer composed of more or less fibers. 

 "When the membrane serves for secreting or excreting purposes, as in 

 the salivary glands or the kidneys, it is usually simple when it serves 

 the mechanical purpose of protecting a part, as over the tongue or skin 

 it is invariably multiple and stratified, the surface wearing away while 

 new cells replace it from beneath. 



(7) In nerves, stellate cells are connected by their rays to each other, 

 or to fibers which conduct the nerve impressions, or they act as recep- 

 tacles and storehouses^ for them, just as the switch board of a telephone 

 system serves to connect the various wires. 



All of these tissues are sui)plied with blood in greater or less quan- 

 tity. The vascularity depends upon the function which the tissue is 

 called upon to perform. If this is great, as in the tongue, the lungs, or 

 the sensitive part of the foot, a large amount of blood is required; if 

 the labor is a passive one, as iu cartilage, the membrane over the 

 withers, or the tendons of the legs, the vessels only reach the periphery, 

 and nutrition is furnished by imbibition of the fluids brought to their 

 surface by the blood vessels. 



Blood is brought to the tissues by arterioles, or the small termina- 

 tions of the arteries, and is carried off from them by the veinlets or the 

 commencement of the veins. Between these two systems are small 

 delicate networks of vessels called capillaries, which subdivide into a 

 veritable lace- work so as to reach th.e neighborhood of every element. 



In health the blood passes through these capillaries with a regular 

 current, the red cells or corpuscles floating rapidly in the fluid iu the 

 center of the channel, while the white or amceboid cells are attracted to 

 the walls oi che vessels and move very slowly. The supply of blood is 

 regulated by the condition of repose or activity of the tissue, and under 

 normal conditions the outflow compensates exactly the sux)ply. The 

 caliber of the blood vessels, and consequently the amount of blood which 

 they carr^'^, is governed by nerves of the sympathetic system in a healthy 

 body with unerring regularity, but in a diseased organ the flow may 

 cease or be greatly augmented. In health a tissue or organ receives its 

 proper quantity of blood ; the nutritive elements are extracted for the sup- 

 liort of the tissue and for the product, which the function of the organ 

 forms. The force required in the achievement of this is furnished by 

 combustion of the hydro carbons and oxygen brought by the arterial 

 blood, then by the veins this same fluid passes off. less its oxygen, 



