614 EXPERIMENTS WITH VIBRATING CILIA. 
carefully dissected from the roof of the mouth, is pinned to a 
board. A piece of skin from near the throat of the frog, and 
from one-third to half an inch square, is placed upon this mem- 
brane with the inner surface in contact with the cilia, it being kept 
in mind that these vibrate from before backwards towards the 
throat. On the skin may be placed a plate of lead of somewhat 
smaller size. This serves as a vehicle to which weights may be 
added at will to increase the load, and also as a drag, to set in 
motion the instrument described farther on. To show the distance 
through which the load is carried, the flag and pointer may be 
used as in the case of the gills before described. Pains should be 
taken to have the board on which the experiment is made perfectly 
horizontal, otherwise a sliding motion, especially when heavy 
weights are used, may come in to vitiate the experiment. 
Although the results are not uniform, the following will give some 
idea of the force exerted, as shown by the time in which and the 
distance through which the weight was carried. The mean of four 
experiments shows that a weight of 1.300 grams was carried 
15mm. in 61.2 seconds, or about 4mm. per second, the weight rest- 
ing on a surface 12mm. square. A weight of thirty-three grams 
resting on the same amount of surface, a mean of four experi- 
ments gave a distance of 6.6mm. per minute. We have seen 
forty-eight grams resting on a surface l4mm. square, moved, 
though very slowly, across the whole length of the membrane, but 
the exact time was not noted. Dr. H. P. Bowditch has repeated 
these experiments in the laboratory of Ludwig at Leipsic with 
even heavier loads. 
Finding that so much force was exerted, the idea of utilizing it 
was naturally suggested, and after various trials the following in- 
strument was devised for this purpose, in which the direct motion 
produced by the cilia was made to give rise to a rotary one. The 
instrument consists of two light toothed wheels (see figure), the 
arger 30mm. and the smaller 5mm. in diameter. To the axis of 
the first is attached a small drum 5mm. in diameter, around which 
is coiled a thread of the finest and most flexible cotton. The axis 
of the smaller wheel is prolonged through the frame in which both 
wheels move, and carries on its end an index made of two bristles 
inserted into a central piece of cork, which is attached to the 
axis. On the end of each bristle is a very light paper pointer. 
The whole length of the index is 110mm. but may be made longer 
