146 OPERATIVE TECHNIQUE. 



dying out. The innate vitalit}' of ancient superstitions is well illus- 

 trated by its having survived so long. 



The chief results of blood-letting are as follows : 



1. The reduction in quantity of the circulating fluid is at once 

 followed b}^ diminished blood-pressure in all the vessels and changes 

 in the circulation favourable to the relief of local congestion. 

 Congestion in important organs like the lungs and brain, and 

 possibly also the sensitive laminae of the feet, therefore constitutes 

 the chief indication for bleeding. 



2. The blood withdrawn contains a large quantity of nutritive 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, the fact renders blood-letting still more question- 

 able as a means of combating inflammation. 



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

 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. In general, therefore, 

 bleeding is seldom resorted to in infective or toxic diseases. The good 

 effects sometimes obtained in lumbago and laminitis may perhaps be 

 referred to the above causes. 



3. 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. 



4. Bleeding is followed by a temporary increase of tissue meta- 

 bolism, 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. 



It would appear that bleeding plays no great therapeutic rule, 

 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. 



