The Microscope. 343 



di-opped upon the slide. For oil of cloves, xylol, and Canada balsam 

 wide-mouthed bottles are used. In the first two bottles are brushes; 

 in the last, the ordinary glass rod. Other necessary utensils are a 

 glass rod, sharp-pointed scissors, clean slips and cover-glasses, filter- 

 paper, twine or coarse thread, a small bottle of absolute alcohol, a 

 sharp, clean needle, a fine, clean rag, and a hand-towel. 



Aside from these, a board, fifteen by five inches, with two pair 

 of holes, large enough for a piece of tape to pass through double, 

 is an essential help. The first pair of holes should be four inches 

 distant from the second, and the two holes of each pair one and a 

 half inches a part. The tape should be so passed through the holes 

 that there will remain upon one side of the board, loops, on the other, 

 long ends, by which, upon passing the extremities of the frog 

 through the loops, one may easily and firmly tie the frog upon the 

 board. Such preparation is necessary, otherwise the manipulations 

 cannot follow one another quickly enough . After these preliminaries 

 have been completed, the labelled bottles being placed within 

 reaching distance, the distilled- water and alcohol in front of these, 

 and the corrosive sublimate nearest of all, we are ready to bind our 

 frog upon the above-mentioned board and begin our preparation. 

 We make use of the frog for this purpose at first, since its blood 

 coagulates less quickly than that of mammals. The vena femoralis, 

 which may be seen as a dark blue line below the knee-joint on the 

 inner side of the leg, having been snipped, we quickly bring with a 

 glass rod a drop of the blood which comes from the wound upon a 

 slip previously moistened by the breath, and throw the whole into 

 the dish of sublimate for six minutes. If a little care is taken to 

 spread out the drop of blood in pu.tting it on the slide, the result is 

 more satisfactory. Brought from the sublimate into the dish of 

 water, we find that the greater part of the blood adheres to the slip. 

 The superfluous sublimate being washed from the preparation during 

 the moment that it remains in the water, we next partially dry the 

 slip by resting it upon filter-paper before dropping it into the 

 alcohol bath. The slip which has remained in alcohol six minutes, 

 is brought again into distilled water for half a minute, since our 

 coloring fluids are water solutions. The hsematoxylin is then 

 dropped upon the slide, and removed again at the end of six 

 minutes by resting the edge of the slip upon filter- paper, and after- 

 wards washing with distilled- water for one minute. The same 

 process follows with the nigrosin and eosin, the first remaining upon 

 the slip for one minute, the second two minutes. From the eosin 



