in the Diagnosis of Blood Stains. 135 



many of the suspected stains occurred on the prisoner's boots, and 

 proved upon that article of clothing singularly easy of detection. 



Finally, I would remind those who demur at the idea of allowing 

 a man's life to hang upon such seemingly insignificant circumstances 

 as a difierence in size of blood-corpuscles, how often the reactions 

 of arsenic, afforded by a quantity of the metal too excessively trivial 

 to be accurately estimated by the most delicate balance, have 

 sufficed to bring out the crime of murder, and to aid in securing 

 that just punishment for violation of law in which we all have so 

 deep an interest, because on it all our enjoyment of life and property 

 depends. 



To the second objection, viz. that the variations above and 

 below the standard size of corpuscles from any particular animal 

 are too great and irregular to permit us to obtain an accurate result 

 by measurement, I would answer, that this difference in size is 

 more especially observable in corpuscles dried in a thin film upon a 

 glass slide, and is then probably in part a pathological change due 

 to external violence in spreading and drying. These variations are 

 comparatively slight in fresh blood, as is proved by the following 

 experiments, made with my -gV^h inch objective, which gives with 

 the micrometer eye-piece an amplification of 3700 diameters. 

 When thus magnified the human red blood-disks appear about one 

 inch and one-eighth in diameter, so that even shght differences in 

 their size can be accurately measured. Among one hundred red 

 corpuscles freshly drawn from five different persons, the maximum, 

 minimum, and mean diameters were as follows : — 



Twenty from a white male aged 30 



>J >5 )> )? ') "'-' 



„ „ „ female „ 44 



,, „ an African „ „ 50 



„ a white male „ 8 



The measurement of twenty corpuscles from part of the first of 

 these specimens dried in a thin film upon a shde gave a maximum 

 of 2 wo-> a minimum of tot> and a mean diameter of ^^^a of an 

 inch. 



Moreover, if it can be shown that the smallest red disks of 

 man, as usually met with in mechanically unaltered blood, whether 

 dry or moist, are larger than the largest corpuscles of an ox, and 

 a fortiori of a sheep, such an objection, as regards these particular 

 animals at least, becomes valueless, and that this is the case I pro- 

 pose to presently demonstrate. 



As illustrating the accuracy which some practical experience in 

 measuring minute objects, hke the red blood-disks, with the cobweb 

 micrometer enables us to attain, I may instance the following fact, 



VOL. xn. L 



