STRUCTURE OF COLORED BLOOD-CORPUSCLES. 65 



Having made a number of measurements, I can state that in 

 every person's blood that I have examined, there are some as 

 small as, or smaller than, the ^grr? an< l ^ n nearly every person's 

 some as large as, or larger than, the zTej ^ an inch in diameter 

 (i. e., .00655 and .00917 mm.), with transitional sizes between 

 these. The extremes are sometimes not met with in each field of 

 a drop, nor even in every drop of a person examined j but I have 

 not found any adult of either sex from whose blood the smaller 

 extreme was absent, and only very few without the larger. I 

 have repeated the measurements of blood-corpuscles without 

 the addition of the re-agent, both with and without oiling the 

 edges of the covering-glass, i. e., with and without preventing 

 the ordinarily rapid evaporation, with practically the same 

 results; drying of course contracts blood-corpuscles, and cor- 

 responding variations are observed. Some of the disks are in 

 outline not perfectly circular ; by measuring the largest diameter 

 of the largest and the smallest diameter of the smallest disks, 

 the extremes I have met with in one and the same specimen of 

 human blood are, as to the smallest, about the goVo? an( l as * 

 the largest, the 2rVo? ^ an i ncn ft- e "> -00422 and .01016 mm.). 

 If the detached globules, which I shall describe, be counted as 

 blood- corpuscles, there are even still smaller ones. In each speci- 

 men of blood, the majority of red corpuscles, however, are of about 

 one size, which differs in different specimens, but is most fre- 

 quently between the ggVT an d the g- T Vo of an inch (.00655 .00819 

 mm.), or somewhere about the ^yo of an inch (.0075 mm.). The 

 calculated average of the size of the red corpuscles in a drop 

 i. e., the arithmetical mean of the measurements is usually a 

 little higher than the size of the majority of the corpuscles. 



A very few, especially the smallest, but occurring exception- 

 ally also among the larger, seem more or less globular ; all others 

 are bi-concave disks, the periphery being more shining and thick 

 than the central portion. 



So-called "rosette" and "thorn-apple" forms may be seen, 

 either immediately or in the course of a little while. I have often 

 watched the individual corpuscles while these forms, and many 

 others, were being produced j and in Part III. of this communica- 

 tion I shall offer an explanation of their production. 



Concentrating our attention upon the shape of the circular 

 disks, we soon find that the round outline of a few (and the same 

 is at times also true of the smooth surface) begins to be made 



