484 BUREAU OF ANIMAL INDUSTRY. 



(7) In nerves, stellate cells are connected by their ra3's to each other, 

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

 tacles, storehouses, and transmitters for them, as the switchboard 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 ever}- element. 



In health the blood passes through these capillaries with a regular 

 current, the red 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 supply. 

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

 which they carry, is governed b}^ nerves of the sympathetic system in 

 a health}^ 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 hj combustion of the hydrocarbons and oxy- 

 gen 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 indicates the 

 process of nutrition of the tissues. 



H3^pernutrition, or excessive nutrition of a tissue, ma}' be normal or 

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



CONGESTION. 



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

 sive 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 Wxcv dui'ing digestion, or in the lungs after severe work, 

 from which, in the latter case, it is shortly relieved by a little rapid 



