246 TJIK BLOOD OF EQUINES. 



With increasing altitudes, however, the erythrocyte count 

 of man rapidly increases, sometimes by as much as two millions 

 and even more. This change is noted very soon after the pei-sou 

 reaches the high altitude, and is undoubtedly the most conspicxi- 

 ous alt-eration in human blood duiing health. Compared with 

 other normal variations this change is remarkable, and mvicli 

 stress is laid upon it in text-books. 



The less conspicuous changes already referred to are accounted 

 for by " sex " in the case of women, and by bad hygienic condi- 

 tions (in the broadest sense) in the case of school children and 

 individuals of the same sex; even age is said to influence the 

 erythrocyte count in man. 



The few available loublislied data about horse blood seemed to 

 indic;ite that the same constancy of erythrocyte count existed. 

 Thus eleven authors, quoted by Burnett in his text-book, give 

 erythrfX'yte counts varying from 6'3 to 8"4 millions per c.mm. 

 The figures now obtained by us, however, prove conclusively that 

 in the horse the erythrocyte count is subject to enormous varia- 

 tions during health — the range being from about 4 to about 13 

 millions per c.mm. 



In the human being in health a range of variation of about 

 2 millions in erythrocyte count is considered remarkable; by com- 

 parison, the range of variatio)i of over 8 'millions observed for the 

 erythrocyte count of healthy horses is really astonishing — and 

 equally astonishing is the fact that sex, hygienic conditions and 

 age have very little, if anything at all, to do with this. More- 

 over, this range was obtained for animals at and about Pretoria, 

 and hence altitude is not a responsible factor. Frei, who worked 

 in this Laboratory some years ago, obtained erythrocyte counts 

 which showed similar variations, but could find no explanation. 



The clue to the correct interpretation of these variations was 

 given by two animals kept under observation for a long time. 

 The first was a riding horse, and its erythrocyte count was always 

 about 9 millions per c.mm. The second horse was permanently 

 stabled, and its erythrocyte count was always about 5i millions. 

 The stabling and the food of each were the same — only the one 

 horse worked, and the other led a life of idleness. 



This clue was followed up by grouping the animals according 

 to the amount of fast work they did as " stabled," " fast work- 

 ing " and " other " horses, the last group including all those 

 horses whose histories were not known. It was then seen that, 

 without exception, every stabled idle animal had a very low 

 erythrocyte count as compared with the higli figure noted for 

 every fast-working horse, and that exercise is therefore a most 

 important factor detei-mining the number of erythrocytes in 

 horses. 



In order to obtain further evidence of this fact some race- 

 horses in full training were bled, and the erythrocyte counts 

 found to be exceptionally high — always in the neighboiu-hood of 



