218 LORANDE LOSS WOODRUFF 
each of about one minute duration, were made for each sample 
and their average taken. This was the general method of observa- 
tion employed, but in samples in which only a few comparatively 
large forms were present the number of each species was counted 
directly under a dissecting lens. Again, in cases in which myriads 
of the tiniest active monads were present it was impossible to 
count them satisfactorily and accordingly it was necessary to esti- 
mate the number present on the basis of the experience gained 
by the use of the exact counting system. In addition to the ob- 
servations made with the compound microscope, in nearly every 
case the sample was also examined with a lens magnifying about 
ten diameters, in order that a comprehensive view of the slide 
could be secured which would serve to indicate the general dis- 
tribution of the organisms on the slide, and act as a check on the 
more exact observations. 
Accordingly, while the enumeration of the organisms varied as 
exigencies demanded, all the counts were made by one person and 
consequently the personal equation of the observer, which must 
influence to some extent the data collected from such a series of 
observations, remained the same. It is believed that the data 
secured are sufficiently comprehensive to give accurately the 
relative number and to show approximately the actual number of 
the various organisms present. It is obvious, of course, that the 
method employed does not give data which show the presence 
in the infusions of one or a dozen organisms. Therefore the terms 
employed, ‘time of appearance’ and ‘time of disappearance,’ 
indicate simply the presence or absence of a sufficient number of 
animals to be detected by the method. More than this, I believe, 
could not be secured without the expenditure of more labor than 
one individual could devote to it daily for a period of three months. 
Obviously the rate of development of an infusion will depend 
upon the temperature to which it is subjected, and, within limits, 
the higher the temperature the more rapidly the sequence of 
forms will proceed.’ The ideal way, therefore, to conduct such 
a series of experiments as these under consideration would be to 
° Wocdruff and Baitsell: The temperature coefficient of the rate of reproduc- 
tion of Paramaecium aurelia, Am. Jour. Physiol., vol. 29, no. 2, 1911. 
