1919] Rhodes: Binary Fission in Collodictyon triciliatum Carter 207 



protozoan technique. I refer here not to Romano wsky 's dry film, 

 which has no general use or approval, but to a modification of Schau- 

 dinn's moist film method, which involves the use of some fixative, 

 pipetting the organisms on to the cover smeared with this and then 

 the evaporation of the water until the animals will adhere to the 

 cover when dropped or floated directly on the surface of the killing 

 fluid. I found on attempting this method that conditions accompany- 

 ing the evaporation process ruptured the body, and normal killing or 

 fixation could not be obtained with Collodictyon, which is evidently 

 more susceptible than many other free living forms. 



Collodictyon when exposed to excessive evaporation may rupture 

 instantaneously or more frequently pass through moribund phases as 

 shown in text figure C. All foreign bodies are ejected, the vacuoles 

 become larger, gradually fuse into still larger pathological vacuoles, 

 which finally rupture. The organism becomes much distorted and 

 disintegration usually takes place along the sulcus. 



Wherever the death rate is above the normal or even at equilibrium, 

 the number of abnormal moribund forms is undoubtedly great. Many 

 life cycles could be and possibly have been built up on such fallacious 

 interpretations. Protozoa may be potentially immortal but the vast 

 majority do not survive. The real problem, therefore, is to find some 

 way to determine the normal from the moribund, either physiologically 

 or pathologically abnormal. 



I resorted to killing en masse, either with or without centrifuging. 

 I found that in lightly centrifuged material there was no nuclear dis- 

 placement or other variations which could be detected from the non- 

 centrifuged, so I adopted the centrifuge as the best and quickest 

 method of running up the material. After a normal killing in a beaker 

 and running up through the alcohols in centrifuge tubes, some of the 

 organisms were then fixed to covers, where it was essential for the 

 quick handling of material, as in Mallory 's stain. I also found it 

 convenient and satisfactory in dehydrating rapidly after certain stains, 

 as in phosphotungstic haematoxylin, to pass from an aqueous stain 

 by adding 3 to 5 c.c. of 50 per cent and then 40 to 50 c.c. of absolute 

 alcohol, immediately centrifuging and adding carboxylol. 



At times Collodictyon was found to be rapidly increasing in num- 

 bers in the aquarium and from this it was judged that there was little 

 or no death taking place, but that conditions were favorable for a 

 maximum growth and normal reproduction. Material collected at 

 such times as this was regarded as normal, at least for the phase of 



