CIRCULATION OF THE BLOOD. 



369 



which are shown hj g gi ff, in order to keep the web open, or 

 what answers better is a series of pegs of the shape repre- 

 sented by h, each having a slit, i, extending more than half 

 way down It ; the threads are wound round these two or three 

 times, and then the end is secured by putting it into the slit, i. 

 The plate is now ready to be adapted to the stage of the 

 microscope; the square hole over which the foot is placed 

 must be brought over the hole in the stage through which 

 the light passes to the object-glass, so that the web can be 

 strongly illuminated by the mirror. The magnifying power 

 employed should be from fifty to a hundred diameters, or 

 the one-inch or the half-inch object-glass. If the individual 

 corpuscles of the blood and lymph are required to be seen, the 

 quarter-of-an-inch object-glass should be used. Those who 

 are not in possession of a brass frog-plate may employ a piece 

 of soft wood or a layer of cork, about six inches long and two- 

 and-a-half wide, for the purpose ; a hole about an inch long 

 and three-quarters-of-an-inch broad, as shown at b in fig. 242, 



being cut through it near 

 to one end. The frog 

 secured in the bag, and 

 tied to the cork in the 

 same way as to the brass 

 plate, is to have the web 

 brought over the hole, b ; 

 small pins, d d d, may 

 then be passed through 

 the web into the cork 

 close to the toes, c c c, to 

 keep it open. This plan, although more easily managed and 

 attended with much less trouble than that represented by 

 fig. 241, is, nevertheless, generally looked upon by the fair 

 sex as a much more cruel act than where the threads are 

 employed. Some persons adopt the plan of tying the bag 

 containing the frog to the plate, in the manner shown by 

 fig. 241 ; but, instead of employing either strings or pins, 

 they spread out the web of the foot upon the glass at the end 

 of the plate ; the animal will generally keep its foot steady 

 24 



Fig. 242. 



