MICROMETRIC NUMERATION OF THE BLOOD-CoRPUSCLES, 143 
. tity of heemo- 
h sasakee us ae Volume of the bare es be ee 
Thorpascle corpuscle, Bd 
pee gr. pw cube. My gr. 
Man . . : ‘ 30 72 04166 
Pigeon . ; 3 : 52 125 0°4160 
Lizard . ; ‘ ; 70 201 0°3483 
Russian frog. : ; 216 629 03432 
Proteus : é : 1066 9200 01159 
the volume of the corpuscles in ° is, however, quite out of 
the question in clinical work, and as no simpler method has 
at present been devised, we must it appears to me, be at 
present content to ascertain the mean area of the corpus- 
cles in w”, and to take as our unit of corpuscular substance py? 
multiplied by the unknown thickness of the corpuscle, on the 
assumption that this is uniform throughout, and always the 
same. Actually we know this not to be the case, as normal 
corpuscles are biconcave and not flat, and in pathological 
conditions they vary in form, and possibly in thickness. 
However, let the constant representing the supposed thick- 
ness (or more accurately the factor by which we should 
multiply the diameter to obtain the volume) be called r. 
Our arbitrary unit of corpuscular substance will, therefore, 
be ru. The results in the way of comparison will only be 
liable to error in so far as the corpuscles vary in thickness. 
As, however, this variation is immeasurable by our present 
instruments, it may be taken that the unit 72 will give for 
all practical purposes a sufficient approximation to the 
truth. 
To obtain the mean area of the corpuscles in any given 
specimen of human blood, the mean diameter of the cor- 
puscles must first be ascertained. A simple method of 
obtaining this is to graduate the microscope so that an image 
thrown by the camera lucida at a certain flxed distance 
magnifies exactly 1000 diameters. The corpuscles having 
been rapidly fixed and dried by exposing them to the action 
of heat, or better still, to the vapour of osmic acid, their image 
is thrown by the camera lucida on to white paper, care being 
taken to correct the errors of refraction.! The outlines of 
the corpuscles are then traced in pencil, and their diameters 
1 “Note sur la Mesure des Grossissements Microscopiques,’ par LL 
Malassez. ‘Correction des Déformations produites par les Chambres 
Claires de Milne-Edwards et de Nachet,’ par L. Malassez. 
