THE BLOOD OF EQUIx\ES.. 249. 



These results (Graphs I to III) leave no doubt that in the 

 ]iors6 the erythrocyte count increases, within limits, iritJi the 

 amount of hard fast work. 



When viewed in the light of the evolutionary history of the 

 horse the results obtained are perhaps not so startling. In the 

 past the horse depended for its very existence upon its speed 

 and endurance, two qualities only possible with a highh'-efhcient 

 sj'stem for carrying oxygen to the tissues. The modem horse 

 possesses a jaotential caj^acity for speed and endurance, and these, 

 as we now see, can be realised by training. During this training 

 the muscular capacity of the animal develops, and concurrently 

 with this the capacity of the blood for caiTying oxygen increases 

 through an increase in the number of normal erythrocytes. 



The influence of work upon the erythrocyte count is really 

 remarkable. The animal kept absolutely without exercise for a 

 sufficient time may show an erythrocyte count of only one-third 

 that of a fully-trained racehorse. This means that about eight 

 million erythrocytes per c.mm. of horse blood may be formed by 

 the tissues purely as a response to work. Does work influence 

 the blood picture in man, and in animals other than equines? 

 The question at least opens a pi-omisiug field for futiu-e investiga- 

 tion. 



Diurnal Variatioxs. 



Many horses were kept under observation for long periods of 

 time, and it was noted that in any individual the erythrocyte 

 count, though fairly constant, showed minor variations, not only 

 from day to day, but even in some cases from hour to hour. At 

 first this was very puzzling, and it was thought possible that 

 such factors as food and water might be responsible. Experi- 

 ments expressly devised for the purpose, however, showed that 

 moderate stai-vation or thirst, followed by food or water, and 

 moderate exercise, did not influence the erythrocyte coiuit in 

 any definite way. 



When blood was taken simultaneously from the jugular vein 

 and the ear, it was found that the count of the latter was almost 

 invariably higher than that of the former, and that the difference 

 was sometimes very great ; the figure for the ear blood being 

 subject to greatest variation. A few of the results obtained are 

 given in Graph IV. Figures 1 to 4 give the data for horses which 

 were given food while excited or immediately upon return from 

 work, and then not disturbed at all excepting just at the time of 

 bleeding. The data in figures 5 to 7 are those for animals that 

 were taken away from food, and then excited by being threatened. 



These results show that the two counts always converge when 

 the animals are excited, and diverge most widely during digestion 

 and rest, and that, as a rule, an increase in the count for ear 

 blood is accompanied by a decrease in the count for jugular blood. 

 Furthermore, in as short a time as 10 minutes the two counts can 

 be made to agree by the mere process of threatening the horse. 

 It is, therefore, not the food, as such, which causes this wide 

 divergence between the two counts. 



