502 VETERINARY PHYSIOLOGY 



the fact that, after an animal or person has inhaled carbon 

 monoxide, it is possible to determine to what proportion the 

 gas has replaced ox3'gen in the oxyhsemoglobin. If, then, 

 an individual breathes a given volume of carbon monoxide, 

 and if a measured specimen of blood is found to contain a 

 definite percentage of the gas, the rest of the gas must be 

 equally distributed through the blood, and thus the amount 

 of blood may be deduced. If, for instance, 50 c.c. have been 

 taken up, and there is 1 per cent, in the blood, the whole blood 

 holding the 50 c.c. must be 5000 c.c. They conclude that 

 the blood is about 2?)' ^ P^i' cent., of the weight of the 

 body in the human subject. This method has been 

 adversely criticised on the ground that the CO may be taken 

 up by the tissues of the body as well as by the blood. 



3. Dreyer has devised another method for the living 

 animal. After bleeding, the volume of blood is restored in a 

 a few minutes by the passage of fluid from the tissues (p. 450). 



The number of red cells per c.mm. is determined, A 

 definite amount of blood is drawn ; and after a few minutes 

 the number of corpuscles is again counted. The reduction 

 indicates the dilution of the blood. Thus, suppose the first 

 count gave 5,000,000 per c.mm., and that 400 c.c. of blood 

 were taken, and that the second count gave 4,500,000 — a 

 fall of 500,000 or 10 per cent. — the 400 c.c. must be 10 per 

 cent, of the whole blood which is thus 4000 c.c. 



4. The vital red method. Vital red is a non-toxic 

 pigment, which forms a colloidal solution in the blood, and 

 does not readily transude from the vessels. By injecting a 

 measured quantit}^ into a vein and determining its dilution 

 in the blood plasma, the total amount of plasma may be 

 calculated, and if the volume of cells is determined by 

 centrifuging in an ha^matocrit, the total volume of blood 

 may be calculated. These last two methods give results 

 corresponding to Welcker's (Practical Physiology). 



As has been shown in the study of circulation (p. 4 50), 

 the total amount of blood in the body does not always 

 correspond with the amount in effective circulation. In 

 such conditions as wound or operation shock considerable 

 amounts of blood may stagnate in the capillaries, and thus 



