128 



THE AMERICAN MONTHLY 



[Jniy, 



the laboratory of the writer by Dr. 

 Tuckerman, of this city, jointly with 

 the writer, and occupied several 

 weeks' time. We worked at it 

 nightly for some three weeks, usually 

 devoting from five to seven hours to 

 the work each evening. Afterwards 

 less time was given to it, but the work 

 was steadily pursued. Of the numer- 

 ous objectives tried, we finally settled 

 upon a homogeneous immersion ^\ 

 by Gundlach, which proved admira- 

 bly suited for the work on account 

 of its relatively great working dis- 

 tance. This quality in an objective 

 is essential in working on stains, 

 though not important for Avork on 

 fresh or spread blood. After trying 

 many processes and media we finally 

 adopted the following method : — The 

 blood stain was scraped with a knife 

 blade and the dust received on a clean 

 glass slip ; to this was added a drop 

 of distilled water and a cover glass 

 was laid on. After three minutes a 

 blotting strip was applied at one edge 

 of the cover and a watery solution 

 of eosin at the other ; after acting one 

 minute this was in like manner drained 

 away and a solution of« chloral hv- 

 drate 40 grains to i ounce applied. 

 As soon as the eosin solution was 

 wholly replaced, the slide was wiped 

 around the cover with a dry blotter, 

 and the cover cemented down with 

 gold size or Folsom's finish, and the 

 mount at once examined. 



Our tests seem to show conclusively 

 that after the chloral is applied no 

 further change takes place in the 

 corpuscles enclosed. Having settled 

 on this method, all the tests considered 

 in reaching a conclusion were made 

 strictly according to it, although it 

 should be noted that all the tests by 

 other methods, and they were many, 

 were entirely corroborative of those by 

 this method. Casting the image of 

 the corpuscles enlarged about 4,500 

 diameters upon a screen was tried, 

 but abandoned as it required too much 

 time and seemed no inore certain than 

 other methods. The difference be- 

 tween the corpuscles of human and 



dog's blood is, however, shown with 

 striking effect by this method. The 

 average human corpuscle will measure 

 about if inches, while the largest 

 dog's corpuscle will hardly exceed 

 i|^ inches, and the average will be about 

 i^ inches (1.357, 1-278, 1.164). 



Although measurements made by 

 the camera lucida, or with the cob- 

 web micrometer, are doubtless suffi- 

 ciently accvn-ate for the purpose, there 

 are theoretical and practical sources 

 of error which, though minute, are 

 not found in the use of the eye-piece 

 micrometer, and the latter was used 

 by us exclusively in the tests relied on, 

 it being removed from its mount and 

 cemented in the eye-piece used, so that 

 the same spaces were always used in 

 making the measurements, having pre- 

 viously determined that the spaces used 

 were exactly equal within the limits 

 of any test we could apply with over 

 a dozen stage micrometers. 



The reagents used were from the 

 same bottles throughout, which were 

 kept corked with scrupulous care ; 

 pipettes were drawn to capillary points, 

 and any change in strength of solu- 

 tions due to evaporation thus guarded 

 against ; in short, we taxed our com- 

 bined ingenuity to secure absolute 

 identity of conditions in all the com- 

 parative tests. The blood of ten dif- 

 ferent kinds of animals was measured, 

 a varying nimiber of each kind, but 

 the greatest attention was paid to that 

 of the dog and luan. Usually 100 

 corpuscles on each slide were meas- 

 ured, an equal number by each of us, 

 25 at a time, thus distributing as 

 equally as possible any effects of per- 

 sonal equation, or variation of the 

 specimen. The average of the 100 

 measurements was then tabulated for 

 comparison. In addition to the meas- 

 urements of known bloods, slides were 

 prepared, in several series, by Dr. 

 Tuckerman, and submitted to me with 

 labels marked with symbols of signifi- 

 cance unknown to me, which speci- 

 mens I would measure and record, and 

 then substitute labels of significance 

 unknown to him and let iiim measure 



