SIZE CHANGES IN NERVE CELL BODIES 313 
measure these types selectively to determine their absolute and 
relative sizes. This is what the writer has always done, and it 
will be clear enough from the sort of information it affords that 
it is the one thing to do. Another thing which might be done, 
as Kocher did, and which has always been done by other investi- 
gators, is to lump all cells irrespective of type and strike an aver- 
age. The uncertainty of this method, which may or may not 
give true results, will be very easily shown through the data ob- 
tained by stage measurements. The employment thereof is the 
one reason for the wide variety of results which has been obtained 
by different workers. 
The stage measurement is frankly a selective measurement, 
but in the sense of the selection of types as they come, not of 
picking cells here and there according to their probable suitability 
to work out right. It can be made, and has been made, as rigid 
in requirement as the aggregate way can be. The cerebellum is 
peculiarly suited for this because one can start at a convenient 
point and follow the line of Purkinje cells around with no danger 
of doubling back until all have been covered. If one then exacts 
the requirement to measure and diagnose according its stage 
every cell in such a median section that its karyosome and the 
trunk of its dendrite are included, he has no more leeway than 
by the aggregate method. 
The requirement of the trunk of the dendrite is specified for 
the following reason in the case of the Purkinje cell. It is 
known to be pear-shaped, which I have confirmed by some fifty 
reconstructions in wax. I am not going to measure such a cell 
unless it is obvious that it is fairly complete in the plane of its 
longitudinal axis, for it would be averaging a spheroidal dimen- 
sion with elongated ellipsoidal ones. 
With a greater or less unequal distribution of stages, the quota 
of a uniform number for each stage will be filled up at different 
points, one by one all becoming full. One simply proceeds 
from section to section, passing over those stages whose quota 
is complete, ‘but adding to the incomplete as they come. Of 
course this will demand many sections when a stage is scanty, 
—for the almost absent resting cells in the exercised puppy it 
took 77. One loses the benefit of that ‘‘cut-with-one-stroke-of- 
