i 7 8 
Journal of Agricultural Research 
Vol. IX, No. 6 
minutes after an 0.8 mile run, and the normal proportions did not return 
for 2 hours. In pigs our counts were made in all cases quite withir 
this time. 
Hawk (5) advances six possible explanations for the increase of 
erythrocytes in exercise. These are (1) the production of new corpus¬ 
cles; (2) concentration of the blood through increased urine formation 
and copious sweating; (3) concentration of the blood through increased 
evaporation in the lungs; (4) concentration of the blood through vaso¬ 
motor contraction and rise in blood pressure; (5) sudden passage into the 
circulating blood of a large number of cells lying in various parts of the 
body and inactive before the time of muscular exercise; and (6) passage 
of fluid from the blood to active muscles. 
Hawk concludes that the number of red corpuscles produced by 
muscular exertion is due primarily to the passage into the circulating 
blood of a large number of cells lying in various parts of the body and 
inactive before the time of the muscular exercise. 
We can hardly see how this is possible in the case of the red corpuscles 
which remain in a closed, constantly circulating system. Further, if 
this conclusion is correct, we would expect an increase in the number 
of erythrocytes in the pig. 
Schneider and Havens (7) conclude that the increase in erythrocytes 
is due to a concentration in the peripheral capillaries. Willebrand (5) 
believes .that the withdrawal of water from the blood by the working 
muscles is the primary cause of concentration. Zuntz and Schumberg 
(5, 7) accept Willebrand’s explanation. 
If either of these conclusions is correct, we would expect the blood 
of the pig to show an increase in the erythrocytes following exercise. 
Tomow (2) concluded that the increase in the red corpuscles corre¬ 
sponded roughly to the increased density of the blood as a result of 
sweat caused by muscular work. Similar conclusions can be drawn 
from the work of Hasselbalch and Heyerdahl (2), since there was no 
definite reaction after the first run, while after the second run there was 
a very distinct rise in the number of red corpuscles. This has been 
explained by Boothby and Berry (2) on the ground that there was no 
distinct change in the relative number of red corpuscles until sufficient 
time had elapsed for an appreciable amount of sweating to have occurred. 
Boothby and Berry conclude from their studies that the increase in 
the percentage of hemoglobin and red corpuscles occurs under condi¬ 
tions of work causing an appreciable amount of perspiration. If no 
perspiration occurs, there is no such increase. 
Evidence in the pig rather tends to confirm this theory, since the pig 
is an animal which does not sweat and does not show any increase in the 
number of red corpuscles under various degrees of muscular exercise. 
The same has been found to occur in the case of the rabbit, another animal 
which does not sweat. 
