1900 - 1 .] Dr J. Y. Simpson on Binary Fission of Ciliata. 405 
Paramecium aurelia , every 24 hours. 
Paramecium caudatam, every 24 hours. 
Oolpidium colpoda, every 8 hours. 
In the second place, we may note that the rate of fission depends 
intimately upon the food conditions to which the creatures are 
subjected. In conducting these experiments I have been in the 
habit of employing two distinct foods — either a hay infusion of a 
light straw colour, into which one put a piece of meat to 
hasten the production of bacteria, or else the forms produced 
by making a very dilute paste with ordinary flour and 
water. Paramecium and Stylonichia take kindly to either of 
these media, of which a drop was added daily to the slide on 
which they were isolated. The conditions were kept as constant 
as possible by the withdrawal of a couple of drops of the 
medium (some four or five drops in all) in which they had passed 
the night, which were replaced by one of food and another of 
distilled water. Pond water was also sometimes employed, but 
greater constancy was secured by the other method. I could not 
find that either of these two food media made any appreciable 
difference on the rate of division. But after a certain amount of 
manipulation one learned that there was a minimum of food that 
kept, e.g ., Paramecia, as they were ; that there was also a definite 
amount, usually one drop, which caused one division in twenty-four 
hours ; and that there was also a maximum which seemed to have 
an inhibitory effect upon the forms in question. In this case the 
body of, e.g., Stylonichia , became positively black with unassimilated 
food matter, a condition of affairs that is reproduced in fig. 1. 
Change to a less rich medium soon resulted in a return to the 
normal state of affairs. 
We may note in the third place that the rate of division bears 
a direct relation to temperature. To Maupas belongs, the credit of 
having established this fact upon a comparatively sound basis. As 
far back as 1776 Spallanzani had observed that the multiplication 
of Ciliata was accelerated by increased temperature. But it is 
Maupas’ chief count against the defective work of his predecessors 
that they had not properly attended — in some cases not at all — to 
the temperature and food conditions. The following rates of 
division under different temperatures are taken direct from Maupas. 
