14 BLOOD. 



calibre of the arteries from disease. General ansemia is the term usually 

 applied to a state of ill-health in which there is deficiency in the number 

 of red corpuscles, deficiency in the amount of hcemoglobin, or deficiency in 

 both of these constituents of the blood. It may be due to the effects of disease, 

 bleeding, purgation, etc. As the ruddy hue of health cannot be present on the 

 cheeks of a person whose blood is deficient in hsemoglobin, aucemic people 

 show their ill health in their faces. But as the skin of a horse is thick, 

 covered with hair, and generally full of pigment, we are unable to judge 

 by his complexion whether or not he is suffering from anaemia. 



CONGESTION may be either passive or active. Passive congestion consists 

 of an accumulation of blood in a part with decreased rate of blood flow, and is 

 caused by (1) diminished action of the heart, as we may see by the swelling 

 of the legs in cases of debilitating di-eases. (2) Want of exercise, especially 

 Avhen aided by the force of gravity acting against the return of the blood, as 

 for instance, in the legs of horses which are kept standing for a long time, like 

 those on board ship. (3) Resistance to the veinous circulation, which we can 

 observe in strangulated hernia (p. 284). As the walls of the veins can be far 

 more easily compressed than those of the arteries, it follows that in strangu- 

 lation of a part, the blood pumped through the arteries is more or less stopped 

 in the veins. (4) Resistance to the arterial circulation. Owing to increased 

 blood pressure and obstruction in the local circulation, the part, as I shall 

 presently try to explain, becomes swollen and lowered in vitality, and will 

 consequently be difficult of cure, if affected by disease or injury, as we may 

 see, for examjjle, in cases of grease or over-reach in chronicallj^ filled legs. 



Active congestion may be due, among other causes, to the exercise of a 

 normal function, as for instance, congestion of the blood-vessels of the stomach 

 and intestines during digestion ; and to anaemia in another part, as in con- 

 gestion of the liver from chill. If continued too long, as in congestion of the 

 lungs, it may lead to inflammation, of which it is always the first stage. 



INFLAMMATION. — Sanderson defines inflammation as " the succession of 

 changes which occurs in a living tissue when it is injured, provided that the 

 injury is not of such a degree as at once to destroy its structure and vitality." 

 It might be defined as the reaction of living tissues after injury ; the term, 

 " living tissues," being applied to all the tissues of the body, except the 

 epidermis (p. 154), which includes the scarf-skin, hair and hoofs. When 

 inflammation is set up, the circulation of blood in the part, at first becomes, 

 as a rule, quickened for a brief space of time ; but soon becomes impeded, 

 until there is more or less complete stagnation of blood. Consequently the 

 blood-vessels become gorged with blood, and owing to the increased pressure 

 there is an excessive escape of plasma and leucocytes into the neighbouring 

 tissues. In health, the amount of this exudation is duly regulated by two 

 opposing forces ; one being the blood pressure derived from the contraction 

 of the lieart ; the other, the tensity of the tissues (Hamilton). Wlien the 

 tissues become less tense from injury (such as a wound, blow, application of 

 a blister, or removal of the skin), the exudation is proportionately increased. 

 In fact, the action of any means (placing our feet in warm wal;er, for in- 

 stance) which will soften the tissues, or which will relieve them of pressure, 

 will be followed by more or less swelling of the part from this cause. The 

 fact of stagnation of blood occurring, will practically mark the transition 

 from congestion to inflammation. We have no exact knowledge respecting 

 the cause of this stagnation of blood in inflammation. The condition of the 

 walls of a blood-vessel seems, however, to have ^ome connection with the 

 stagnation of blood in it; for according to Cohnheim's experiment, if we 

 expel the blood from the ear of a rabbit, for example, and keep the part, by 

 ligature or other means, bloodless for some time, inflammation will be set 

 up in it, on the blood being again allowed to fill the vessels. 



As the filtering power of the walls of the capillaries varies inversely as the 

 blood pressure in them ; the exudation of inflammation is rich in fibrin-pro- 



