EXPLANATION OF PLATES 
PLATE 13 
Fig. 1. All-metal cage for mice or rats. 
Fig. 2. Top view of cage and apparatus for recording automatically 
the time of birth of litters of rats or mice. The floors are removed and 
are seen at the right, the larger from above, the smaller (which carries 
the nest, an inverted strawberry box, see pl. 14) from below. 
ABBREVIATIONS 
blk.—adjustable block. 
b. p.—binding post through which the levers are connected to one pole 
of battery. 
fl. sup.—metal support attached to under side of floor and resting on slender 
pin driven into side of lever bar (p. br.). 
Ir. sup.—metal support for fulerum of lever. 
p. br.—paired bars of lever. 
s. br.—single bar of lever which carries the counterweight (wt.). 
tr.—truss-like frame attached to floor to prevent tipping of latter. 
tr. br.—transverse bar of lever 
up.—upright posts which support the wire sides and top of the cage inde- 
pendent of floor. 
wr.—wire connecting platinum contact (pl. pt., fig. A) through the ful- 
crum nail (ful. nl., fig. B) and one of the metal supports (Ir. sup.) 
with the binding post (b. p.). 
wt.—counterweight. 
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