56 
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Variation in Chilomonas 
Biitschli (1883-87, Taf. XIV, Fig. 9 c). When the infiisorian life begins to disappear 
from a culture it usually means that the organisms are encysting rather than dying. 
That this is the case is clearly shown by the fact that by appropriately changing 
the culture medium they may be induced to reappear again in the active condition. 
This fact is, of course, well known to all who have worked to any extent with 
Protozoa. 
For the present purpose it is not of immediate consequence to know what the 
optimum conditions for infusorian life are, or, on the other hand, in what manner 
the cultural conditions become so unfavourable as to lead to the encystment of 
these organisms. It is of course a well-known phenomenon that laboratory 
cultures usually and normally pass through both these stages. The important 
investigation of Peters (1904) in this field indicates clearly that the basis of the 
matter lies in the changing chemical constitution of the culture medium. From 
the present standpoint it is sufficient to note that the " favourable" conditions of 
Culture B and the " unfavourable " conditions of Culture A were in no way 
artificially or experimentally induced, but appeared in a normal way in the 
undisturbed cultures. 
With reference to the technique used in the collecting and measuring the 
following may be said. Samples were taken from each of the cultures with a clean 
pipette quite at random. These samples were then killed with Worcester's 
formol-sublimate fluid (Pearl, 1903). This fluid has been used by the writer in a 
number of biometric studies on Protozoa, and has proved very satisfactory for the 
purpose. With Chilomonas it is possible to prove that killing with this fluid when 
properly performed produces no measurable distortion of the organism. After 
killing, the specimens were measured by the camera lucida method which has been 
used by the writer and his students in other similar studies. (Cf for description 
of methods. Pearl and Dunbar, 1903, and Pearl, 1906.) The magnification used in 
the present instance was such that 1 mm. on the cards on which the dimensions 
were pricked with a needle point corresponded to 1"45 mikrons (= x 6897 linear). 
The measurements are given in mikrons. 
The characters measured were length (C — D) and greatest breadth (A — B) of the 
body as shown in Figure 1. An attempt was made to measure the flagella, which 
A 
Fig. 1. Outline of Chilomonas to show measurements taken. 
appear with perfect distinctness in specimens killed with the formol-sublimate 
fluid, but it was not feasible on account of the too frequent curvature of a flagellum 
either up or down in the line of sight. In addition to the absolute length and 
