ZOOLOGY AND BOTANY, MICROSCOPY, ETC, 1105 



which present on the one hand crystalline resemblances, and on the 

 other more nearly ai)proach in their appearance and character the low 

 and obscure forms of vegetable life. 



The author also records the fact that, after chloroform, the 

 blood plasma exhibits escaped vesicular forms, and perhaps more 

 abundantly than in typhoid and other febrile conditions. 



Measurement of Blood-corpuscles.* — Dr. M. D. Ewell has en- 

 deavoured to determine whether there is a constant average size of 

 the human red blood-corpuscles, so as to render it possible by means 

 of micrometric measurements to distinguish human blood from that of 

 domestic animals. 



He used two accurate standards, one consisting of lines ruled on 

 speculum metal 1/2000 in. apart, by Prof. W. A. Eogers, a Bulloch 

 cobweb eye-piece micrometer and a 1/10 in. Spencer hom. imm. 1 • 35 

 N. A., with a Bausch and Lomb achromatic amplifier giving an ampli- 

 fication of about 1500 ; also Prof. H. L. Smith's immersion fluid. 



An examination of the tabular statement of results shows that the 

 difference between the greatest and smallest averages of 25 corpuscles 

 is 0-000028 or 1/35714 in., a magnitude that may be easily measured 

 by any person having the requisite skill and apparatus. 



The difference between the highest and lowest averages of 50 

 corpuscles is 0-000015, or 1/66666 in., which approaches more 

 nearly the limit of micrometric measurement, though probably not 

 beyond it. 



The difference between the highest and lowest averages of 75 

 corpuscles is 0-000012, or 1/83333 in., which ajiproximates the limit 

 of micrometric measurement. 



The difference between the highest and lowest averages of 100 

 corpuscles is 0-000009, or 1/111111 in., which is within the limits 

 of personal and instrumental error, " according to the highest living 

 authority upon this subject," who writes, in substance, that it is easy to 

 measure 1/50,000 in., but to be sure of 1/100,000 in. is not possible. 



The conclusion to bo deduced from the above figures is obviously, 

 Dr. Ewell says, " that, when a sufiicient number of corpuscles are 

 measured, there appears to be an average size which varies within very 

 narrow limits, which may possibly be accounted for, or, at least, is 

 consistent with personal and instrumental errors ; for, though I have 

 carried out the figures to the sixth decimal place, 1 have not the pre- 

 sumption to declare that the results can be relied upon further than 

 the fifth place, and have carried out the figures to the sixth only to 

 insure accuracy in the fifth so far as possible. Another conclusion 

 is, that granting for the moment tliat it is possible to identify blood 

 by meuKurement of the red corpuscles, of which 1 am by no means 

 Butisfiod, it is reckless in the last degree, if not criminal, to express 

 an opinion upon tljc measurement of less than 100 corpuscles. To 

 express an oi)iuion upon the measurement of only 10 corpuscles, 



* The MicroHfopo, v. (18S.">) i>ii. 183-G. Aiucr. Moii. Micr. Jouiii., vi. (18s5) 

 p. 150-1, from 'Chicago Legal Nuwd.' 



