4 BULLETIN" 1349, U. S. DEPARTMENT OF AGRICULTURE 
similar curves, representing the daily egg-laying rate of various 
individual queens. Brunnich's work, unlike Dufour's, is based, not 
on an actual count of each cell containing brood, but on a mathe- 
matical calculation of the number of such cells derived from linear 
measurements of the brood area on each frame throughout the 
season. From data thus obtained daily egg-laying rates are cal- 
culated for the whole season. Although the claim can not be made 
that Briinnich's work is as nearly accurate as Dufour's, the Swiss 
investigator has adopted a method which is fairly speedy and readily 
utilized, and which gives results reliable enough for most purposes. 
METHOD 
In 1920 work on this problem at the Bee Culture Laboratory was 
first begun when Lloyd K. Watson, formerly apicultural assistant, 
made actual counts weekly of all eggs, larva?, and sealed brood in 
five colonies for the entire season. Any such method of counting 
brood on each comb is necessarily slow.' In cool weather it involves 
the possibility of brood becoming chilled before the operation is 
completed; at other times there is danger of robbing, and in any 
event there is too long a disturbance of the colony. Accordingly, 
when the writer took over the work at the beginning of the season of 
1921, a photographic method was determined upon, whereby photo- 
graphs are taken weekly of every frame containing sealed brood, and 
counts are made later from the negatives. Only sealed brood is 
counted, because of its greater clearness on the negatives. As a 
result of the use of this method, photographic records of 16 colonies 
were obtained in 1921, and of 32 colonies in 1922. Adding to these 
the counts from the five colonies in 1920, the equivalent of a total of 
53 individual seasonal brood-rearing records has been obtained 
already from the work now in progress. 
A small building adjacent to the apiary not only houses the camera 
permanently but also affords protection from robber bees while 
taking the pictures. During exposures two 500-watt electric lamps 
furnish light sufficient to obtain good negatives at all times within 
the building, regardless of conditions of light outdoors. The camera 
itself is fastened securely to one end of a base made of 2-inch plank. 
To maintain the brood frames firmly in position during exposures 
and yet to have in the negative an image of every cell on the exposed 
side of each comb, a substantial holder (Plate I, A) is used which 
consists of a base with two uprights at each end, the uprights being 
joined by a top piece. The width of the holder is such that the lower 
half of each end bar of a Langstroth frame just fits into a groove extend- 
ing upward from the base on the inner surface of each upright. A 
super spring fastened to the rear edge of each groove presses the end 
bar firmly against the front edge, and thus the brood frame is held 
rigidly in a definite position, although it may easily be slipped in 
and out of the holder. The holder itself is fastened securely to the 
same base as is the camera, but at such a distance from the lens as to 
give a reduction to a scale two-thirds that of the original. Because 
of the uniform focal distance and the uniform illumination, all 
negatives are made on an identical scale and under the same light 
conditions. By the aid of a suitable device attached to the frame 
holder there is photographed with each frame of brood a record 
showing the date, the hive and hive body from which the frame came, 
