MICROMETRIC NUMERATION OF THE BLOOD-CORPUSCLES. 133 
very simple. The solution of blood, after being well shaken 
in the Mixer, is drawn up into the tube by capillary attrac- 
tion, and the number of corpuscles contained in the given 
length of the tube is counted. This is 
rendered extremely easy by the aid of the 
small squares of the ocular micrometer. 
The number obtained is multiplied by 
the denominator written, as already men- 
tioned, on the glass plate, and the pro- 
duct multiplied by 100 or 200, according 
to the strength of the solution used, gives 
the number of the corpuscles per cubic 
millimeter. Thus, supposing that, in a 
length of 500u, the volume =~, of a 
cubic millimeter, and that a 1 per cent. 
solution occupying this space contains 
300 corpuscles, then 
300 x 150 x 100 = 4,500,000 
the number of corpuscles per cubic mil- 
limeter of blood. The calculation, how- 
ever, is not so simple as this in prac- 
tice, since the multiplier, of course, will 
seldom be a round number. 
M. Ranvier, in his ‘ Traité Technique 
d’Histologie,’ says that this method, con- 
sidering the short time it takes, gives, of 
all those hitherto known the best results. 
It is certainly very accurate, but it has 
two great disadvantages. In the first 
place, owing to the necessity of under- 
taking the somewhat difficult task of gra- 
duating the microscope, the same Compte- 
Globules must always be used with the 
same microscope and the same lens ; hence 
its use clinically is obviously very much 
curtailed. Secondly, the extreme deli- 
cacy of the instrument is a serious draw- 
back. Though a person with ordinary 
manipulative skill may learn to use this 
instrument, it requires more than ordinary 
WiGeae 
care to keep the minute capillary tube absolutely clean 
and this is positively necessary, since a minute particle of 
dirt, or a few dried corpuscles left in the tube, will vitiate 
the accuracy of the results. My own experience is that, 
though I am able to make correct observations with this 
