1880.] ■ 



MICROSCOPICAL JOURI^AL. 



57 



for the dog, was somewhat smaller 

 than the average of all I had re- 

 corded for man. Yet, some of the 

 averages I had found for lifty or a 

 hundred, or even more canine cor- 

 puscles were larger than the smaller 

 averages obtained for human blood ; 

 indeed, occasionally rivalled the 

 larger. I mentioned further that I 

 agreed with the view of L'Perier 

 {Bull, des Travaux de la Soc. de 

 Pharm. de Bordeaux. 1877 ; p. 

 282 et seq.), that the blood of quite 

 young dogs (up to a month or two 

 old) more frequently contained very 

 large corpuscles, and gave averages 

 equal to those obtained from human 

 blood, than was the case with older 

 animals. I had, since the trial com- 

 menced, mounted several slides of 

 the blood of a pup three weeks old, 

 in which corpuscles measuring 400- 

 millionths (^-gVo ) of an inch in di- 

 ameter were by no means rare (I 

 may add that I have these slides 

 and will take pleasure in showing 

 such corpuscles to any competent 

 microscopist). Fifty corpuscles on 

 one of these slides gave an average 

 of 326-millionths of an inch ; forty 

 coi-puscles on a slide from another 

 pup of the same age, gave an 

 average of 320-millionths of an 

 inch ; while twenty corpuscles from 

 the blood of a full grown dog gave 

 an average of but 300-millionths of 

 an inch. Measured with the same 

 instruments, fifty corpuscles of my 

 own blood gave an average of 324- 

 millionths ; forty from another in- 

 dividual gave an average of 327- 

 millionths ; twenty from another 

 gave an average of 316-milliontlis. 

 I added that all these measurements 

 were made with a new Zeiss ho- 

 mogeneous immersion ^ and a 

 cobweb micrometer, the power be- 

 ing such, that each division of the 

 micrometer-wheel equalled t-^oVcto 

 of an inch. Every corpuscle in the 

 group selected was measured, each 



being first brought to the centre of 

 the field for the purpose, and those 

 corpuscles which appeared to be 

 other than perfectly spherical, were 

 measured in the long and short 

 diameters, and the mean taken. In 

 short, every known precaution was 

 employed to secure accuracy. 



In view of all the foregoing con- 

 siderations, I did not think the 

 microscopist is warranted in at- 

 tempting to distinguish on oath, 

 between human and canine blood, 

 even on preparations carefully made 

 from fresh blood. If he makes a 

 supposition based on the average 

 size of fifty or a hundred corpuscles, 

 he will no doubt (jften come out 

 right, but he will also occasionally 

 come out entirely wrong ; and the 

 difiiculties in the case of corpuscles 

 soaked out from dried stains, are of 

 course still greater. 



CORRESPONDENCE. 



A DEVICE FOR MOUNTING. 



To THE Editor: — I have recently 

 devised and applied to my Cox turn- 

 table, a simple device which I find 

 to be of much use, especially when 

 mounting in glycerine. In brief, it is a 

 slender arm of brass which is attached at 

 one end to the hand-rest of the turn-table 

 by a milled-head screw. The other end 

 extends over the centre of the turn- 

 table at a suitable height above it. 

 A pointed screw comes down through 

 the end of the arm exactly over the 

 central dot. In mounting in glycerine, 

 for example, after the cover is ap- 

 plied to the object, the slide is transferred 

 to the turn-table, the cover is brought to 

 the centre and the pointed screw is turned 

 down upon the cover, compressing the 

 object and expelling the superfluous fluid. 

 After a rough cleaning a ring of gelatine- 

 solution may be applied, as directed in 

 Marsh's Treatise on Scction-Cuttiitg, p. 

 41. After a couple of applications of the 

 gelatine and time allowed for it to set, the 

 screw may be loosened and the slide re- 

 moved from the turn-table. 



This little piece of apparatus may not 



