14- BLOOD. 



ANjEMIA or bloodlessness may be either local or general. In the former 

 case, it may, as we have just seen, be owing to congestion in other parts ; 

 and can also be brought about by cold, pressure, and diminution of tihe 

 calibre of the arteries from disease. General anaemia 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 hseraoglobin, c(r 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, 

 anaemic 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 "■ 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 diseases. (2) Want of 

 exercise, especially when 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 

 venous circulation, which we can observe in strangulated hernia (p. 282). 

 As the walls of the veins can be far more easily compressed than those of 

 the arteries, it follows that in strangulation 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 obstruc- 

 tion 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 example, in 

 cases of grease or over -reach in chronically 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 the congestion 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. — ^Inflammation is 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, is at first, 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 get 

 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 

 heart ; the other, the tensity of the tissues. When 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 water, 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 tihis 

 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 some 



