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S. C. BROOKS 
de Khotinsky's cement to the bottom of a glass dish 6.5 cm. in di- 
ameter and 1.5 cm. deep. The strips were held horizontally in such a 
position that as the free end bent it moved back and forth horizontally. 
Immediately after the strips of peduncle were cut, they were put 
in place in the glass dish and covered with 20 cc. of an isotonic solution 
of the salt to be investigated. The dish was then covered with a 
glass plate and set on the stage of a microscope. The glass plate 
was pierced by an opening just large enough to allow the introduction 
of the front of the Bausch and Lomb 2/3 inch objective, by means of 
which, in combination with a No. 7.5 ocular, provided with an ocular 
Fig. I. 
micrometer, the position and rate of movement of the free end of the 
strip was determined. Figure I shows the arrangement of the appa- 
ratus. 
The epidermal surface of the strip furnished a sharply defined 
point of reference. The evaporation from a dish so covered, with the 
objective in place, amounted to about 0.05 percent per hour at room 
temperature; this amount was not sufficient to have any appreciable 
effect on the time required for recovery. 
A solution was considered to be isotonic with the cells of the 
tissue when there was a barely perceptible decrease in the curvature 
of the strips of peduncle immediately following their immersion in the 
solution. This condition signified that the solution was actually 
