April, '23] 
NOLAN: TWO-YEAR BROOD CURVE 
119 
accurate idea may be formed from such evidence as to what really takes 
place in brood-rearing throughout an entire season. 
In America as early as 1859, Baldridge had conceived the idea of 
determining the egg-laying rate throughout the season by periodic 
counts. He actually made one such count of all the eggs, larvae, and 
sealed brood in each frame of a certain hive. The task was evidently 
too arduous, inasmuch as it was not continued further. Nevertheless 
the report of this single count as published in the first volume of the 
American Bee Journal (1861) forms the earliest available brood census. 
It was nearly forty years later before anything of real value appeared 
on this problem. In 1895 Baldensperger published in Gleanings in 
Bee Culture some estimates made throughout the active season at in¬ 
tervals of from two to four weeks of the amount of brood in a given 
colony in Palestine. It must be admitted that, although these estimates 
are not absolutely accurate, they do furnish a fairly reliable index of what 
in general takes place throughout the year. This seems to be the first 
published work giving the results of periodic counts or estimates for 
such a length of time. Previously, as already stated, the results for a 
total season were mere calculations based simply on the results of a 
single count at the height of egg-laying activity. 
The year 1901 marks an epoch in such investigations because at that 
time Dufour in the Annuaire de la Federation des Societes Frangaises 
d'Apiculture published the results of actual counts of brood made at 
intervals of twenty-one days from 1897 to 1900 inclusive, a period of 
four years. In the first three years he used two colonies, and in the 
fourth year only one colony. The magnitude of this work may be rea¬ 
lized when it is borne in mind that Dufour actually counted each egg, 
larva, and sealed cell. 
In 1919 Brunnich published in Der Schweizerische Bienen-Zeitung the 
brood curve of a single colony for the year 1918. His work, unlike 
Dufour’s, is based, not on an actual count of each cell containing brood, 
but on a mathematical calculation of the number of such cells derived 
from linear measurements made throughout the season of the brood 
area on each frame, the number of cells in any chosen linear unit being 
well known. 
Such in brief were the few outstanding attempts to throw light on 
the subject before 1920. In that year work was begun in this field at 
the Bee Culture Laboratory. For this purpose in 1920 five colonies, in 
1921 sixteen colonies, and in 1922 thirty-two colonies were used. In 
1920 weekly counts were actually made of all brood, both sealed and un- 
