164 THE PRACTICE OF VETERINARY MEDICINE. 



is impeded, it is called mechanical congestion, and passive 

 congestion is when the blood circulates in a sluggish 

 manner. To have health there must be a regular and not 

 far-distant supply, a right state and composition of the. 

 blood, proper nerve force, etc. The blood should move in 

 a regular and even manner through the arteries and veins, 

 the red corpuscles most abundant in the centre of the stream, 

 and moving faster than the white. When the nerve stimulus 

 is proper, a certain amount of contraction of the blood- 

 vessels persists, and the circulation of the blood is regulated 

 thereby. When the nerve stimulus is increased to any 

 great extent, the vessels appear to be paralyzed, and instead 

 of contracting, they dilate ; exudation of white, and Some- 

 times of red, corpuscles takes place through the walls of the 

 capillaries, the white corpuscles being called leucocytes. 

 When the vessels dilate, the blood rushes into them, the 

 circulation becomes slower and slower, and inflammation is 

 finally set up. 



Inflammation is manifested by heat, pain, redness and 

 swelling. The heat is due to the amount of blood that is 

 sent to the part, as well as to certain changes which are 

 taking place in the blood itself. The heat is more apparent 

 to the sufl'erer than to the observer ; it is more sensibly in- 

 creased, and becomes more apparent to the examiner, when 

 the inflammation is remote from the centre of circulation. 

 Pain is a characteristic symptom of inflammation, a good 

 example being in laminitis, in which the pain is excruciating. 

 In pneumonia, the horse very often appears to be suffering 

 pain only in a very slight degree, if at all, even in cases 

 where the inflammation is suflaciently severe to cause death. 



Eedness depends upon the quantity of blood sent to the 

 parts ; sometimes it is a dark red with streaks in it, at other 

 times a bright red or florid colour is observed, in which 

 case the inflammation is of the most acute type. Swelling is 



