THE BLOOD OF EQUINES. 251 



During the digestion most of the blood is diverted to the 

 splanchnic areas, and peripheral circulation becomes slow. 

 During excitement the blood pressure is raised, and the peripheral 

 circulation is more vigorous. The two counts thus agree best 

 when the circulation is vigorous, and least when the peripheral 

 circulation is sluggish. It is thus the mechanical state of the cir- 

 culation that influences the erythrocyte count, the distribution of 

 the erythroc^'tes being most uniform when the circulation is very 

 active. The concentration of tlie erj^throcytes in the ear blood 

 with a sluggish circulation is probably due to relative increase in 

 lymph formation, and possibly in some instances to sedimenta- 

 tion. The daily and even the hovuly variations in erythocyte 

 count of jugular blood are now readily understood. They depend 

 upon the mechanical state of the circulation rather than upon 

 other factors. 



Techmque. 



The technique employed may be summarised thus. Blood 

 drawn from the jugular vein excej^t when specially taken else- 

 where, was collected in 10 c.c. bottles containing a measured 

 adequate amount of sodium citrate solution. From this was deter- 

 mined : (a) The percentage volume of erythrocytes by centrifuging 

 in specially prepared uniform tubes of 12 c.c. capacity, blown out 

 slightly at the sealed end to facilitate rapid sedimentation, (b) 

 Coipuscle count after diluting 1 in 200 with Hayem's fluid for 

 erythrocytes, and 1 in 10 with 0'5 per cent, acetic acid for leu- 

 cocytes, the Biirker chamber being vised in both cases. 



From numerous observations expressly designed to determine 

 the degree of accuracy of methods in use, it was concluded that 

 (a) the centrifuge gives very accurate and consistent data, (b) 

 erythrocyte counts are liable to an error of up to 10 per cent, even 

 with the improved Biirker chamber, (c) leucocyte counts are 

 less liable to eiTor. 



The Leucocytes. 



The physiology of these cells is not fully understood, but two 

 functions may be mentioned as illustrating their importance ; 

 some of them act as " soldiers " and ingest bacteria that tiy to 

 invade the organism while others ingest pieces of broken-down 

 tissue and thus act as " scavengers " in the body. 



The number of leucocytes per c.mm. of horse blood is very 

 variable between individuals, the range so far observed being from 

 about 5 to about 20 thousand. In the same individual the leu- 

 cocyte count as a rule remains fairly constant over short periods 

 of time, but sometimes varies quite considerably. In numerous 

 experiments it was found impossible to influence the leucocyte 

 count in a constant manner by such factors as moderate star- 

 vation or thirst, with food or water following. In one series of 

 experiments, however, in whicli a horse was exercised, consistent 



