SIZE OF THE RED CORPUSCLES. 381 



scopic measurement. But it is still more difficult in the case 

 of the micrometer. Harting* and Welckerf- have, on this 

 account, detailed special methods by which the measurement 

 of blood corpuscles may be accomplished. 



As a rule, only the size of those blood corpuscles should be 

 compared, which have been obtained by the same observer 

 with the same instrument. It is self-evident also, when all 

 the foregoing remarks are fully taken into consideration, that 

 only those measurements are serviceable for comparison, in 

 which an exact statement is made of the conditions under 

 which they have been made. 



Hence we must be on our guard respecting the inconsiderate 

 employment of the various tables that have been published on 

 the size of the blood corpuscles in different animals. J The 

 absolute dimensions obtained by Welcker with a micrometer, 

 are 





For man on an average expressed in millimeters : 



Min Mar. 



Diameter of disk . . . 0-00774 (0-00640 0-00860) 

 Greatest thickness of the disk 0-00190 



In six males and three females a minimum was observed of 

 0'0045 millimeter, and a maximum of O0097, all occurring be- 

 tween the terminal values, the smallest excepted, being very 

 nearly of equal size. 



The measurements were made on the corpuscles of fresh 

 blood, or of blood dried in thin layers on glass. 



The measurements given by Welcker for the small red corpus- 

 cles, described by Max Schultze, are 0*005 O006 millimeter ; 

 and from these, gradual transitional forms may, according to 

 Max Schultze, be traced up to those of ordinary diameter, from 

 0-008 to 0-010 millimeter. 



We are indebted to Welcker for exact measurements of the 



* Das Mikroskop, etc., Band ii., p. 288, et seq. 

 t Zeitschrift fur rationelle Medicin, 3 R., Band xx., p. 259. 

 | The most extensive tables on this subject are to be found in Milne 

 Edwards, loc. cit., p. 84. 

 Loc. cit., p. 263. 



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