BLOOD AND BONE-MARROW OF FROG 439 
DESCRIPTION 
a. The histology of the circulating blood 
Though the study was begun in the reverse order, it seems 
preferable to pass from a description of the blood to that of the 
marrow. The cellular elements include the following types 
which will be described in the order enumerated: erythrocytes, 
lymphocytes, eosinophilic leucocytes, basophilic leucocytes, 
neutrophilic leucocytes, and thrombocytes. 
1. The erythrocytes. 'The typical elliposidal, centrally nucle- 
ated, discoid erythrocytes of amphibia are well known and need 
no special description for this species of frog. However, certain 
atypical forms, comparable to those previously specified for cer- 
tain turtle bloods, should again be noted, namely, larger, smaller, 
and senile types and their transition forms. The largest type, 
comprising a relatively small number of cells, is approximately 
one and a quarter times the average size; the smallest type, like- 
wise including only a few cells, may be less than half the average 
size; these are generally stoutly oval with a spheroidal nucleus 
situated nearer one pole; the senile type (fig. 3) is relatively 
abundant in the frogs kept under laboratory conditions over 
winter; this cell has a large, spheroidal, lilac-colored nucleus and 
an expansive shell of very faintly-staining cytoplasm. The 
typical erythrocyte (figs. 1 and 2) has a much smaller oval nu- 
cleus which stains deeply blue, and a greenish-yellow cytoplasm. 
Account must of course be taken of the fact that in smear prep- 
arations the cells are spread out under varying pressures and 
tensions which operate to produce definitive size variations; 
nevertheless, the above-enumerated atypical forms occur in 
some degree. ‘This classification agrees in general with that of 
Werzberg” except that he makes no mention of the senile forms. 
2. The lymphocytes. Under this head may be listed a relatively 
large group of mononuclear leucocytes, varying greatly in size, 
but with the same nuclear and cytoplasmic characteristics. The 
smallest are but slightly larger than the nucleus of a thrombo- 
cyte, with a scarcely perceptible shell of basophilic cytoplasm 
(fig. 4); the largest (fig. 9) have a diameter approximately twice 
