465 



(6) Warm climate and summer heat. — Warmth of the atmosphere re- 

 laxes tbe tissues ; it demands of the auimals less blood to keep up their 

 own body temperature, and the extra quantity accumulates in the 

 bloodvessel system. It causes sluggishness in the performance of the 

 organic functions, and in this way it induces congestion, especially of 

 the internal organs. So we find founders, congestive colics, and stag- 

 gers more frequent in summer than in winter. 



(7) Previous congestion. — Whether the previous congestion of any 

 organ has been a continuous normal one, that is, a repeated functional 

 activity, or has been a morbia temporary overloading, it always leaves 

 the walls of the vessels weakened and more predisposed to recurrent 

 attacks from accidental causes than perfectly healthy tissues are. Thus 

 a horse which has had a congestion of the lungs from a severe drive is 

 apt to have another attack from even a lesser cause. 



The alterations of congestion are distention of the blood vessels, ac- 

 cumulation of the cellular elements of the blood in them, and effusion 

 of a portion of the liquid of the blood into the fibrous tissues which 

 surround the vessels. Where the changes produced by congestion are 

 visible, as in the eye, the nostril, the mouth, the genital organs, and on 

 the surface of the body in white or unpigmented animals, the part ap- 

 pears red from the increase of blood ; it becomes swollen from the 

 effusion of liquid into the sponge-like connective tissues ; it is at times 

 more or less hot from the increased combustion ; the part is frequently 

 painful to the animal from pressure of the effusion on the nerves, and 

 the function of the tissue is interfered with. The secretion or excre- 

 tion of glands may be augmented or diminished. Muscles may be 

 affected with spasms or may be unable to contract. The eye and ears 

 may be affected with imaginary sights and sounds. 



PASSIVE CONGESTION. 



Passive congestion is caused by interference with the return of the 

 current of blood from a part. 



Old age and debility weaken the tissues and the force of the circulation, 

 especially in the veins, and retard the movement of the blood. We 

 then see horses of this class with stocked legs, swelling of the sheath 

 of the penis or of the milk glands, and of the under surface of the belly. 

 We find them also with effusions of the liquid parts of the blood into 

 the lymph spaces of the posterior extremities and organs of the pelvic 

 cavity. 



Tumors or other mechanical obstruction, by pressing on the veins, retard 

 the flow of blood and cause it to back up in distal parts of the body, 

 causing passive congestion. 



The alterations of passive congestion, as in active congestion, consist 

 of an increased quantity of blood in the vessels and an exudation of its 

 fluid into the tissues surrounding them, but in passive congestion we 

 have a dark thick blood which has lost its oxygen, instead of the rich 

 combustible blood rich in oxygen which is found in active congestion. 

 11035 30 



