1905.] the Infecting Organism of Convoluta roscoffensis. 67 



remain colourless and may be kept in this condition for at least a month 

 without showing any sign of infection, whilst at any time batches of them 

 may be caused to become green in one to three days by the addition of sea- 

 water or of cultures of the infecting organism. 



2. The Cultivation of the Infecting Organism. — All attempts to cultivate 

 green cells taken from the body of Convoluta have failed. Haberlandt made 

 an unsuccessful attempt, we ourselves were equally unsuccessful, and so also 

 was Miss Harriette Chick, who brought to the task great experience of such 

 researches and the most recent methods. 



The problem had therefore to be attacked from the other end. If the 

 green prisoners of Convoluta never escape alive, the only chance of obtaining 

 the infecting organism lies in catching it before its entrance into the animal. 

 A scrutiny of many attempts to obtain colourless Convoluta in large quantities 

 revealed the fact that generally egg-capsules, isolated in sterile water, give 

 rise to Convoluta which remain colourless for a fairly well-marked period 

 of two or three weeks. After this time, however, green specimens make 

 their appearance. Sometimes the number of green animals thus appearing 

 is few ; more often it increases with great rapidity. Such results suggested 

 that the infecting organism occurs sporadically on or in the capsules ; that 

 it divides freely in this situation ; and that after a period of vegetative 

 division it is liberated in sufficiently large numbers to infect the hundreds 

 of Convoluta experimented upon. 



During the past summer this hypothesis has been put to the test and 

 found to be correct. Large numbers of egg-capsules were kept in filtered 

 water and the young Convoluta upon hatching were removed, so that the 

 vessels contained only empty capsules or capsules the eggs of which had 

 failed to hatch. These vessels were kept under observation. At the end of 

 three weeks several minute spherical bodies of a spinach -green colour were 

 detected. Upon microscopical examination these proved to be colonies of 

 green cells enclosed by and filling an egg-capsule. During examination 

 the membrane around such a colony bursts, and the contents, previously 

 quiescent, swarm out of the capsule, revealing themselves as so many 

 unicellular flagellated green organisms. 



It remained to apply the infection test. Samples of colourless Convoluta 

 reared in sterilised surroundings were put into the vessel containing these 

 flagellated cells. They became infected, and in the course of two or three 

 days exhibited in their tissues green cells identical in character with those 

 of normal Convoluta roscoffensis. 



Similarly, sterilised sea-water containing cultures of these green organisms 

 is as potent as ordinary unsterilised sea-water in producing infection. 



F 2 



