738 THE AMERICAN NATURALIST.  [Vou. XXXII. 
obtained which can be used for comparison of all waters. Not 
until the invention of such a method can accurate and valuable 
comparisons be made. 
At the basis lies the method of collecting the organisms from 
an accurately determined quantity of water. An ideal method 
is one which includes the concentration of the organic matter 
in a known quantity of water into a smaller known quantity of 
water, which quantity should be a convenient multiple of the 
original quantity. In the process not even the smallest of the 
bacteria should be lost. Counting and enumeration of indi- 
viduals and species is necessary, together with an estimation 
as accurate as possible of the volume of the water, of the inor- 
ganic matter, and of the organic amorphous débris (plant and 
animal). The counting can best be done by the Sedgwick- 
Rafter method (Rafter, G. W., '92). By this method a fairly 
accurate idea can be formed of the comparative volumetric and 
numerical proportions between the three main elements involved 
in the biological study of water ; víz., the living organisms, 
organic amorphous débris, and inorganic substances (silt, gases, 
_ and substances in solution). It would seem that the necessary 
data must be based ultimately upon the counting method until 
such time as means can be devised for separating the living 
organic from the dead (both organic and inorganic) substance, 
and for determining the amount of each. In considering the 
quantity of living organisms not only the number but also the 
size of the individuals must be taken into account. Professor 
Hensen introduced the counting methods for the purpose of 
determining the economic yield of the ocean in the same way 
as the farmer determines the useful yield of his fields and 
meadows, the annual production of grass and grain. Professor 
Haeckel in stating his objections to this method said : “ The 
farmer determines the yield of his meadows, garden, and field 
by quantity and weight, not by counting the individuals. If 
instead of this he wished to introduce Hensen’s new exact 
method of determination, he must count all the potatoes, ker- 
nels of grain, grapes, cherries, etc., not only that but he must 
also count the blades of grass in his plot, even every individ- 
ual weed which grows among the grain of his field and the 
