THE MICROSCOPE. 213 



then, in turn, wash it out with the mercurial solution. Place a little 

 oil around the edge of the glass, to prevent evaporation, when you 

 are ready for inspection. 



For restoring corpuscles found dried upon fabrics, much the 

 same process is observed, save that the dried particles composing 

 the clot are finely pulverized, by means of the needle, allowed to 

 fall upon the slide, a cover-glass placed over them, the under side 

 having been breathed upon, when the solutions are applied at the 

 edge and allowed to run under by capillary attraction. 



Does the clot, so prepared, contain human red corpuscles or 

 those of the dog? 



Place the slide under a good homogeneous immersion objective 

 — a tenth or twelfth is recommended — and, with a one-half or one- 

 quarter eye-piece, make your observations as follows: 



1. Note the average size of the corpuscles. 



2. The thickness of the cell-walls. 



3. The expansibility of these walls. 



Applying a good eye-piece micrometer — cobweb, preferred — 

 being sure that the ruled spaces on glass or dial are evenly spaced, 

 it matters not what the value, in parts of an inch or millimeter these 

 spaces may be, nor whether the corpuscles measure -g-^Vo" or ttVtt °f 

 an inch by any standard but your own. What do they measure, in 

 spaces on your evenly ruled micrometer — how many spaces does the 

 corpuscle occupy? Select one hundred of the roundest of them, 

 and note carefully their value, in spaces, on your scale. If they do 

 not fit a given number of your ruled spaces, lengthen or shorten 

 your draw tube until an average number do fit. Make a record of 

 these lines, length of draw-tube, eye-piece and objective used, and 

 apply, afterward, the same conditions precisely, to corpuscles of 

 known origin, that the difference may be noted. In the examina- 

 tion of human blood, you will find a few smaller corpuscles and a 

 still smaller number of larger ones than the sample will average. 

 Repeat your observations several times, finally compare your results 

 with those obtained from previous examinations of the blood of 

 human subjects, as well as of various dogs, under precisely similar 

 treatment — the results having been carefully noted at the very 

 instant the observations were made. Also compare the specimen 

 under suspicion with that taken from several individuals and dogs,* 



*I compare also with mounted slide of the blood of a large variety of human beings and 

 dogs. 



