THE BLOOD 



amount of this seems to increase with age, even equalling 5 or 6 per cent, 

 of the whole Hb content of the body. This is a source of error. The 

 more muscular animals with darker flesh have more Hb in their 

 muscles e.g., hare more than rabbit, duck than fowl. It is claimed 

 by authorities who have made careful experiments by the bleeding 

 method that this is really the more exact, and that the quantity of 

 blood in an animal bears a definite relationship to the amount of the 

 body surface. These observers used oxygenated Locke's fluid to 

 wash out the circulatory system, and so avoided the transference of 

 tissue fluid into the blood. 'B=W n / k where B is the blood- volume 

 in cubic centimetres, W the weight of the body in grammes, n 0-70 - 0-72, 

 and k a constant (calculated from experiments) determined for each 

 species of animal. The body surface is usually calculated from the 

 body weight by the formula S = &.W| (0-70 0-72 is more accurate 



Descent 



6 lZ 15 18 Zl 24 27 '30 ' 

 Accent 



15 Ifl 



TaC - = Total *yg en Capacity. 

 FIG. 18. EFFECT OF HIGH ALTITUDE ON BLOOD. (Dreyer and Wai ker.) 



than ^). The smaller and lighter animals, which have a relatively 

 greater body surface than the heavier ones, have also a relatively 

 greater blood- volume. This agrees with their relative rates of body 

 heat loss and metabolism, and also with the sectional areas of their 

 tracheae and aortae and weight of heart muscle. A wild -rabbit, con- 

 tains 25 per cent, less blood and 25 per cent, more haemoglobin in its 

 blood than a tame rabbit of the same weight. A wild-hare contains 

 double the blood-volume, 30 per cent, more haemoglobin, and three 

 times more heart muscle than a wild -rabbit of the same weight. No 

 doubt the same kind of difference exists between an athlete and 

 sedentary worker. 



In travellers to high altitudes the blood becomes concentrated 

 and the oxygen capacity increased (Fig. 18). The concentration 

 happens in the first day or two, and is due to withdrawal of plasma. 

 After some weeks the number of corpuscles and the total amount of 



