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or organ receives its proper quantity of blood; tlie 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 hydro-earbons 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 indicates the 

 I)rocess of nutrition of the tissues. 



Hyper-nutrition or excessive nutrition of a tissue maybe normal or 

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



CONGESTION. 



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

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

 face which temporarily foUovv^s a violent muscular effort, or, as in the 

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

 from which, 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 acUve or 

 X>assive. The former is produced by an increased supply of blood to 

 the part, the latter by an obstacle preventing the escape of blood from 

 the tissue. In either case there is an increased supply of blood, and as 

 a result increased combustion and augmented nutrition. 



Active congestion is caused by: 



(1) Functional activity.— Any organ which is constantly or exces- 

 sively used is habituated to hold an unusual quantity of blood; the 

 vessels become dilated; if overstrained the walls become weakened, 

 lose their elasticity, and any sudden additional amount of blood 

 engorges the tissues so that they can not contract and congestion 

 results. Example: The lungs of a race horse, after an unusual burst 

 of speed or severe work, in damp weather. 



(2) Irritants.— Heat, cold, chemical or mechanical. Any of these, 

 by threatening the vitality of a tissue, induce immediately an aug- 

 mented flow of blood to the part to furnish the means of repair— a 

 hot iron, frostbites, acids, or a blow. 



(3) Nerve influence.— This may produce congestion either by acting 

 on the partreflexly, or as the result of some central nerve disturbance 

 affecting the branch which supplies a given organ. 



(4) Plethora and sanguinary temperament.— 'F\\\\-h\oo(iQ(i animals 

 are much more predisposed to congestive diseases than those of a 

 lymphatic character, or those in an ansemic condition. The circula- 

 tion in them is forced to all parts with much greater force and in 

 larger quantities. A well-bred, full-blooded horse is much more 

 subject to congestive diseases than a common, coarse, or old worn-out 

 animal. 



