STUDY OF PELOMYXA. PALUSTRIS. 381 



The years 1897 and 1898 had to be entirely devoted to another 

 bacteriological research, published in 1898, and it was not, there- 

 fore, till the spring of 1899 that attention could again be given to 

 the study of Pelomyxa. 



In April 1899 the interesting discovery was made at tlie 

 University Museum, Oxford, of a very large quantity of Pelomyxa 

 paliistris in a tank in the grounds of the Department of 

 Comparative Anatomy, and my best thanks are due to the Linacre 

 Professor for his great courtesy and kindness in not only placing 

 at my disposal what was practically an unlimited supply of 

 material, but affording me an opportunity of working at this in 

 his laboratory, where most of the following research was 

 accordingly carried out. It may be interesting to note that the 

 colony in the tank must almost certainly have originated from 

 stray individuals accidentally emptied into this tank by me 

 during my researches as a student under Prof. Lankester in 

 1893. The specimens now found were full-fed healthy individuals, 

 and most were of unusually large size, and contained abundance 

 of rods and refringent bodies ; they were generally of a dirty 

 olive-green tint, which, though probably due to food, was found 

 to be characteristic of all really healthy sj)ecimens ; only starved 

 or sickly ones ever exhibit a milk-white appearance. 



It was now determined to undertake a fresh series of culture 

 experiments, side by side with more elaborate study of the 

 bacteria in a great number of fresh preparations, and, if possible, 

 to check the cultures by comparison Vv^ith stages which might be 

 discovered in the fresh preparations. It appeared that only in 

 this way could one be certain of the correctness of results obtained 

 in culture, as an insuperable difficulty to complete sterilization 

 presented itself during the study of this batch of Pelomyxce. 

 This was the fact, not sufficiently realized either by myself or 

 Mr. Hill on previous occasions when we bad only a few individuals 

 to work with, that even if complete sterilization of the outside 

 of a Pelomyxa could be effected, a number of bacteria other than 

 the rods in question v/ere always present in the interior of the 

 animal, having been ingested with the food, and these could not 

 possibly be eliminated without killing the rods. Fortunately 

 for the experimenter, these accidental bacilli did not at all closely 

 resemble the rods, being very much finer and thinner ; therefore 

 there was no difficulty in identification under the microscope. 



The theory I had i'ormed was that single rods might settle 



