152 
The Application of 
actually made in hundredths of an inch, which with ahout 1000 
diameters would correspond to ahout hundred-thousandths, yet the 
measures when corrected by the true magnifying power seldom 
remained a whole number, and the fraction is expressed by an addi- 
tional decimal. 
The measurements of human blood are from twenty-two nega- 
tives, taken from nine drops of blood obtained from eight indi- 
viduals, the whole number of corpuscles measured being 1766. 
The maximum size measured was 396 millionths of an inch in 
diameter. But two corpuscles of this great size were measured. 
The smallest corpuscle measured was 216 millionths of an inch in 
diameter, and but a single corpuscle of this minute size was 
measured. 
The number of corpuscles on each negative ranges from 50 to 
140, except on a single negative, which presents only 26 corpuscles. 
This happens to be a group of large corpuscles, the mean diameter 
of which is 343 millionths of an inch, being the largest average 
diameter obtained on any negative. The smallest average was 
309 millionths of an inch, being the mean of 90 corpuscles. 
The measurements of dog's blood are from thirteen negatives, 
taken from five drops of blood, each from a single individual. The 
largest corpuscle measured was 378 millionths of an inch in diameter ; 
the smallest, 237 millionths of an inch. The negatives contain 
from 80 to 175 corpuscles each, the total number of corpuscles 
measured being 1571. The largest average size for any negative 
was 340 millionths of an inch, being the mean of 100 corpuscles. 
The smallest was 296 millionths of an inch, being the mean of 111 
corpuscles. It will be observed that on seven of the negatives of 
dog's blood the corpuscles have an average diameter smaller than 
the corpuscles on any of the negatives of human blood, while on 
the other six the average size of the corpuscles proves to be larger 
than the smallest average for human blood, and the largest average 
on any one negative of dog's blood exceeds that for any negative of 
human blood except the very largest. I call attention also to the 
very diverse averages obtained with both the human and dog's 
blood from different parts of the very same drop. 
The measurements of guinea-pig's blood are from four negatives 
only, made from different parts of a single drop of blood. The 
total number of corpuscles measured was 401. One of the nega- 
tives gives an average one-millionth of an inch smaller than the 
smallest average for human blood; all the others give averages 
larger than the smallest for human blood. The variations in size 
are not so great as in the negatives either of dog's blood or of human, 
but, as they are taken from a single drop, it can hardly be assumed 
that this is a characteristic feature of the blood of the guinea-pig. 
I think no one could have told from the examination of this drop of 
blood whether it belonged to the guinea-pig, the dog, or man. 
