Differential Cell Counts of the Pituitary in the Thymus Treated Strain of Rats

In an attempt to ascertain the possible mechanism of the previously reported acceleration in the rate of growth and development of rats produced by injections of thymus extract, differential cell counts of the pituitary, in a series of rats have been made, at intervals between birth and 45 days of age, the period of most rapid growth.

All rats (test and controls) were killed with ether, the pituitaries removed as soon as possible, weighed immediately, fixed in Helly's fluid embedded in paraffin and sectioned horizontally; interrupted serial sections were made and stained by a modified Mallory's stain. Slight overstating emphasizes the acidophils and made counting easier. No attempt was made to record finer histologic differences in the cells, although all counts were made under oil-immersion with a Zeiss ocular net micrometer.

As far as possible, the same procedure was followed in making a count; one begins at one lateral aspect of the anterior lobe, as near the “equator” as possible and counts approximately 500 cells while moving toward the center of the gland; this is repeated from the opposite edge of the gland; about every 3rd oil immersion field is counted. A second section is then counted in the same manner, distant about 50 or more micra from the first in the smaller animals, farther in the larger. At least 2000 cells per pituitary per animal are reported; in two instances, once in the female thymus group and again in the male control, the percentage differences in acidophils betwen the first two sections counted were 10.1 and 10.5 respectively. In these two animals 2000 more cells were counted and the average of the total 4000 cells reported.

With these exceptions differences between consecutive counts in the same pituitary are quite uniform.