484 DISEASES OF THE HORSE. 



receptacles, storehouses, and transmitters for them, as the switch- 

 board of a telephone system serves to connect the various wires. 



All of these tissues are supplied 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 hoof, a large amount of blood is required ; 

 if the labor is a passive one, as in cartilage, the membrane over the 

 withers, or the tendons of the legs, the vessels only reach the periph- 

 ery, 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 lacework so as to reach the neighborhood of every 

 element. 



In health the blood passes through these capillaries with a regular 

 current, the I'ed cells or corpuscles floating rapidly in the fluid in the 

 center of the channel, while the white or ameboid cells are attracted 

 to the walls of the 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 sup- 

 ply. The caliber of the blood vessels, and consequently the amount 

 of blood which they carry, is governed by nerves of the sj^mpathetic 

 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 support of the tissue, and for the product, which 

 the function of the organ forms. The force required in the achieve- 

 ment of this is furnished by combustion of the hydrocarbons and 

 oxygen brought by the arterial blood, then by the veins this same 

 fluid passes off, less its oxygen, loaded with the waste products, which 

 are the result of the worn-out and disintegrated tissues, and of those 

 which have undergone combustion. The above brief outline indi- 

 cates the process of nutrition of the tissues. 



Hypernutrition, or excessive nutrition of a tissue, may be normal or 

 morbid. If the latter, the tissue becomes congested or inflamed. 



CONGESTION. 



Congestion is an unnatural accumulation of blood in a part. Ex- 

 cessive accumulation of blood may be normal, as in blushing or in the 

 red face which temporarily follows a violent muscular effort, or, as in 

 the stomach or liver during digestion, or in the lungs after severe 

 work, from wdiich, in the latter case, it is shortly relieved by a little 

 rapid breathing. The term congestion, however, usually indicates a 

 morbid condition, with more or less lasting effects. Congestion is 



