CHIEF RESULTS OF BLEEDING. 141 



It would appear that venesection plays no great therapeutic role, 

 and when we recall that it is contra-indicated both in extreme youth 

 and age, in constitutional weakness, pregnancy, etc., there is little 

 wonder if it is now comparatively little practised. Its most important 

 indications are in dangerous conditions resulting from marked dis- 

 turbance of circulation in important organs like the lungs and brain. 

 It is also valuable in other diseases like laminitis and lumbago, in 

 which, however, its exact modus operandi is obscure. It is known 

 that the reduction in quantity of the circulating fluid is at once 

 followed by diminished blood-pressure in all the vessels and changes 

 in the circulation favourable to the relief of local congestion. The 

 blood withdrawn contains a large quantity of nutritive material and 

 , blood-corpuscles, both of which are of great importance to the 

 organism when struggling with microbic infections ; in such diseases, 

 therefore, blood-letting is seldom advisable. As it is also known 

 that inflammatory processes in the body most commonly result from 

 infection, this fact renders blood-letting still more questionable as 

 a means of combating inflammation. 



On the other hand, a certain amount of infective or toxic sub- 

 stances is also removed with the blood, but as general bleeding 

 weakens the patient, and as active resorption from the great body 

 cavities follows, it may happen that a greater amount of injurious 

 material is eventually absorbed than is removed from the circulation. 



„As mentioned, active absorption from the tissues and body 

 cavities follows bleeding, and the fluid constituents of the blood are 

 thus replaced. This explains the value formerly attached to the 

 practice as a means of promoting resorption. In opposition to this 

 is the fact that the proportion of water in the blood is thereby 

 relatively increased, and with it the tendency to fresh exudation. 

 Experience shows, in fact, that little can be expected of bleeding 

 in this direction. 



Bleeding is followed by a temporary increase of tissue metabolism, 

 as shown by augmentation in the quantity of nitrogenous compounds 

 and phosphoric acid voided in the urine. Such a result can scarcely 

 be interpreted as favouring recovery. 



At the present day horses and cattle are almost invariably bled 

 from the jugular vein ; formerly it was the custom to bleed from 

 the subcutaneous thoracic vein in diseases of the chest, from the 

 mammary vein in diseases of the udder, and from a digital 

 vein in diseases of the foot, but experience slowly convinced operators 

 that no advantage was thus gained. The jugular vein is now almost 

 invariably chosen because it is easy to find, conveniently situated 



