150 



THE AMEKICAN MONTHLY 



[August, 



can commend it, for convenience 

 and rapidity of action, in the highest 

 terms. 



o 



Measurement of Blood Corpuscles.* 



For some time past I have been en- 

 deavoring, for my own satisfaction, to 

 determine w^hether there is a constant 

 average size of the human red blood 

 corpuscles, w^ith the viev^ ultimately 

 to determine whether it is possible, 

 by means of micrometric measure- 

 ments, to distinguish human blood 

 from the blood of domestic animals. 



In order that the results arrived at 

 may be compared with those of other 

 observers, I think it proper to state at 

 the outset the methods and instru- 

 ments employed. 



The first requisite is obviously a 

 correct standard of length, and the" 

 accurate determination of the value of i 

 the eye-piece micrometer used. This 

 preliminary work has engaged much 

 of my time and attention for several 

 months past, and I have finally suc- 

 ceeded in obtaining two very accu- 

 rate standards. The one of these 

 which has been used as the stand- 

 ard of the measurements hereinafter 

 given consists of lines ruled by Prof. 

 W. A. Rogers, of Cambridge, Massa- 

 chusetts (who is recognized as the 

 highest authority upon questions of 

 this sort) , upon speculum metal at in- 

 tervals of I-2000 inch. The relative 

 and absolute corrections of this stand- 

 ard have been determined by Prof. 

 Rogers with very great accuracy, and 

 the value of a division of the eye- 

 piece micrometer described below 

 was determined by taking an arithmet- 

 ical mean of a long series of measure- 

 ments of diflerent intervals of 1-2000 

 inch, so as to eliminate as nearly as 

 possible all errors of graduation and 

 of measurement, and the value of one 

 division of the micrometer was thus 

 found to be .0000009925 or, approxi- 

 mately, i-ioooooo inch. The stand 

 used, with mechanical stage and Abbe 

 condenser, was made by Mr. Walter 



* From advance proofs of the Chicago Legal News. 



H. Bulloch, of this city, and is of the . 

 pattern styled by him the ' biological 

 stand.* 



The actual tube length was 8.91 

 inches from end of nose-piece to up- 

 per end of draw-tube. 



The cob-web eye-piece micrometer 

 used was also made by Mr. Bulloch, 

 the pitch of the screw being ^ milli- 

 meter, and the micrometer head being 

 divided into 200 parts, which were 

 read to i -10 of a division. 



The objective used was a homoge- 

 neous immersion i-io, made by H. 

 R. Spencer, of Geneva, N. Y., hav- 

 ing a numerical aperture of 1.35, and 

 it was used with a Bausch & Lomb 

 achromatic amplifier, giving an ampli- 

 fication of about 1,500 diameters. 

 The immersion fluid used was Prof. 

 Smith's new homogeneous immersion 

 fluid, the composition of which he 

 has not yet made public. 



The blood was drawn from my 

 finger, and a thin film spread with a 

 needle upon the side of a cover-glass 

 from .150 to .165 of a millimeter in 

 thickness, and examined at once, a 

 fresh sample being used upon each oc- 

 casion. It was examined with cen- 

 tral illumination, and always under 

 as nearly the same conditions as pos- 

 sible. During the first four days of 

 the examination, I took, night and 

 morning, about one drachm of the 

 elixir of calisaya, iron, and strychnia ; 

 during the rest of the time no drug 

 was taken, and the conditions were 

 nearly identical each evening. From 

 25 to 100 corpuscles were .examined 

 each evening, and I have tabulated 

 the results, giving the smallest, 

 largest, and average size, in millionths 

 of an inch, of each 25 corpuscles ; 

 also the average of each 50, 75, 100, 

 and 200 corpuscles. The corpuscles 

 were measured, large and small, as 

 they presented themselves in the field 

 of the microscope, the only condition 

 being that they should be approxi- 

 mately circular. 



[The tabular statement of results 

 is omitted, as the summary given be- 

 low is quite sufficient. — Ed.] 



