GIANT-CELLS OF BONE-MARROW 289 
But the giant-cells of the red marrow of the femur of a guinea- 
pig of 400 grams’ weight, from which 10 ce. of blood had been 
taken directly from the heart, were after five days of regenera- 
tive activity on the part of this marrow not essentially different 
from those of normal marrow. 
I then resolved to try the effect of a twice-repeated bleeding. 
From a guinea-pig weighing 420 grams, 10 ce. of blood was 
taken directly from the heart on December 23rd. On January 
8th another 10 cc. was removed. Before killing this animal 
four days later 12 cc. of blood was removed, in order to free the 
marrow as far as possible from circulating blood. Hemopoietic 
activity was intense in the femur, but the giant-cells again gave 
no evidence of active participation in the erythrocytogenic 
process. 
It was then decided to experiment with pigeons. The special 
point of value of this material seemed to be the absence of 
giant-cells in the red marrow. It seemed reasonable to suppose 
that possibly the increased posthemorrhagic hemogenic demands 
might stimulate the potential giant-cell progenitors to develop 
into genuine megakaryocytes, with erythrocytogenic capacity. 
Two pigeons of 300 grams’ weight were aspirated; from one 5 ce. 
of blood was removed, from the other 8 ce. The first was killed 
four and one-half days later, the second five days later. The 
marrow from these femurs showed intense hemopoietic activity, 
but no giant-cells were discernible. 
From the results of these experiments I draw the conclusion 
that sublethal experimental hemorrhage is not an adequate con- 
dition to stimulate intracellular erythrocytogenesis in giant- 
cells of the red bone-marrow of the guinea-pig and the rabbit, 
nor to induce giant-cell formation in marrow normally lacking 
such elements, as in the pigeon. Apparently the intense hemo- 
poietic activity obtaining normally in the yolk-sac is not the 
specific factor which induces the slight erythrocytogenic activity 
of the giant-cells of this hemopoietic organ. The fact that a 
similar activity on the part of these cells occurs in certain patho- 
logic marrows, for example typhoid marrow, suggests that the 
causative factor may be the presence of a toxic agent following 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 27, NO. 3 
