The Microscope. 113 



SELECTIONS. 



MEASUREMENTS OF BLOOD CORPUSCLES. 



Respecting the alleged uncertainty of expert testimony in 

 this department of legal medicine, it is possible that the follow- 

 ing measurements may be of interest to the readers of the 

 Legal News. 



The human blood from which these measurements were 

 made was obtained from the finger of Mr. Henry L. Tolman 

 April fi, 1885, spread in a thin film on two thin cover glasses, 

 and measured within an hour thereafter by M. Tolman and 

 Marshall D. Ewell, M. D., at their respective homes, and no 

 comparison of results was made until the work was completed. 



Fifty corpuscles were measured on one slide by Mr. Tol- 

 man, and twenty-five on another slide by Dr. Ewell. 



Mr. Tolman's measurements were made with a Spencer 

 homogeneous immersion 1-10 objective, numerical aperture 

 127, a f inch eye-piece, a Rogers eye-piece micrometer ruled to 

 1-1,000 inch, and the value of each division was determined 

 from a Roger's stage micrometer, ruled on glass to 1-2,000 inch. 



Dr. Ewell's measurements were made with a Spencer 

 homogeneous immersion 1-10 objective, numercial aperture 

 135, a Bausch & Lomb achromatic amplifier giving about 2,000 

 diameters, a Bullock cobweb eye -piece micrometer, each divis- 

 ion of which represents an absolute movement of 1-400 milli- 

 meter (1-10,000 inch), and is equal to 1-1,000,000 inch on the 

 stage. The value of a division was determined from a Rogers 

 stage micrometer 4-10 inch long, ruled to 1-200 inch, the cor- 

 rection for the entire length being 3-1,000,000 inch at 62 degrees 

 Fahrenheit. The tube length was 8.91 inches. 



Tolman 



EWELL- 



N umber 

 Corpuscles. 



Diameter, Diameter. 



Largest. 



Smallest. 



1-2709" 1-3522" 



1-2817 1-&521 



Average. 



1-31.19" 

 1-3188 



The difference between 1-3,138 and 1-3,139 equals 1-9,850,- 

 182 inch ; or in other words the results are practically identical. 

 While of course, these measurements have no tendency to 

 prove the possibility of identifying blood by the diameter of 

 the corpuscles, they are admissible to show that under exactly 



