1912 Long: Living Eggs of Rats and Mice 109 
tipping by means of the truss-like supports (fr.) attached to 
their under sides. To the angle of each truss is attached one 
end of a light bar (/t. br.), the other end of which is pivoted 
to the base board. The excursion which each lever may make is 
controlled by the adjustable block (blk.) at the end of the un- 
paired bar (pl. 14, fig. 3). By shifting the counterweights the 
alee “ful. ni. 
Fig. A. Diagram of side view of larger part of cage floor with its lever 
and accessories. 
Fig. B. Plan (top view) of one lever shown in side view in figure A. 
blk., adjustable block; p. br., paired bars of lever; ful. nl., fulerum nail 
of lever; fl. sup., floor support of metal attached to under side of floor and 
resting on slender nail (nl.) driven into the side of p. br.; lr. sup., support 
for fulerum of lever; [t. br., light bar for steadying floor; m. 7l., main floor 
of cage; nl., nail; pl. pt., pl. pt... platinum points which make an electrical 
contact with each excursion of the lever; s. br., single bar of lever which 
carries the counterweight (wt.); tr., truss-like frame attached to bottom 
of floor to prevent tipping of floor; tr. br., transverse bar of lever; wt., 
counterweight. 
floors may each be so balanced that they will be moved by a very 
light weight. 
The movements of the floors are recorded on the drum of a 
chronograph by electrical means. The marking apparatus con- 
sists of two small signal magnets (fig. C), which are adapted to 
the purpose by reversing the position of the parts in one and re- 
moving its supporting bar. The arrangement is shown in figure 
C and plate 15. One end of the wire of each coil is grounded in 
