1900] MICROSCOPICAL JOURNAL. 21 



The possibilities of this class of photo-micrography for 

 real work or recreation only, are very great ; the field 

 boundless. I trust that others may feel inclined to enter 

 upon it. A. M. S. 



Micrometry of Human Red Blood Corpuscle. 



FRANK JUDSON PARKER. 



The commonly accepted average diameter of the red 

 blood corpuscle of man is 1-3,200 in. or 7.9 microns, and 

 although some observers have given smaller averages and 

 some have reported larger measurements, no marked dis- 

 tinctions have been discovered between the corpuscles of 

 different races or different nationalties. The cause of dif- 

 ferences reported by various writers is attributed by Dr. 

 M. C. White, to the different amounts of the corpuscle 

 measured. Some rejecting all the dark border, others 

 measuring one-half the dark border, while others include 

 the whole of the dark border on both sides in their meas- 

 urements. 



Prof. Cabot, in his recent book on Human Blood, calls 

 attention to a statement by Gram that ♦'Measureriients 

 published by observers living in Southern Europe are 

 smaller that those of Northern Europe, viz : Italians, 7 

 to 75 microns ; Germans, 7.8 microns ; Norwegians, 8.5." 



To further investigate this question, I have made the 

 measurements reported below. The measurements have 

 been made using Bullock's microscope, with a ^ inch ob- 

 jective made by Spencer and an Abbe condenser, Zent- 

 mayer's cobweb micrometer eye-piece and a stage micro- 

 meter by Leitz, ruled to 1-100 millimeter. This gave for 

 each turn of the screw of the micrometer 6.85 microns, 

 and as the screw head was graduated to 100 divisions, the 

 micrometer is calculated to measure to 0.0685 microns or 

 about 1-350.000 of and inch. 



Each preparation of blood measured was placed upon 

 a glass slide, dried and covered with thin glass. 



