464 



loaded with the waste products, which are the result of the worn out 

 and disintegrated tissues, and of those which have undergone combus- 

 tion. The above brief outline indicates the process of nutrition of the 

 tissues. 



Hyper-nutrition or excessive nutrition of a tissue may be normal or 

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



CONaESTION. 



Congestion is an unnatural accumulation of blood in a part. Excessive 

 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 stom- 

 ach 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 breath- 

 ing. The term congestion, hosvever, usually indicates a morbid condi- 

 tion, with more or less lasting effects. Congestion is active or passive. 

 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 in- 

 creased combustion and augmented nutrition. 



Active congestion is caused by : 



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

 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 injlnence. — This may produce congestion either by acting 

 on the part reflexly, or as the result of some central nerve disturbance 

 affecting the branch which supplies a given organ. 



(4) Plethora and sanguinary tenqjeranient.—F all-hlooded animals are 

 much more predisposed to congestive diseases than those of a lymphatic 

 character, or those in an ausemic condition. The circulation 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 dis- 

 eases than a common, coarse, or old worn-out animal. 



(5) Fevers. — In fever the heart works more actively and forces the 

 current of blood more rapidly; the tissues are weakened, and it requires 

 but a slight local cause at any part to congest the structures already 

 overloaded with blood. Again, in certain fevers, we find alteration of 

 the blood itself, rendering it less or more fluid- which interferes with its 

 free passage through the vessels and induces a local predisposition to 

 congestion. 



