The Parasitology of Pyorrhoea alveolaris. 193 



scraped off with a platinum loop were removed to a fresh jelly. 

 A loopful of a diluted broth-culture of Bacillus jluorescens non- 

 liquefaciens was added, and the plate incubated anaerobically. After 

 four days' incubation the plate was removed from the anaerobic 

 chamber and the amoebae were allowed to encyst. Hydrochloric 

 acid was again added, and loopfuls of cysts were taken from the 

 edges of the culture and placed on a fresh plate, and B. fiuorescena 

 added. The plate was incubated anaerobically for a week, and then 

 removed and allowed to encyst It was then submitted to a bac- 

 teriological analysis, and, if found pure, sub-cultures were made on 

 to slopes in test-tubes, which were then incubated in the anaerobic 

 chamber. All strains of this amoeba appeared to be identical. 



Life-Cycle (Plate XVII). 



Having thus obtained pure mixed cultures which were the 

 progeny of single cysts, it was thought desirable to endeavour to 

 work out the life-cycle by continuous observation. The special 

 live-slide devised by one of us (A. H. D.) was used for this 

 purpose. If the cysts be placed on such a slide, and either 

 incubated, or kept on a warm stage, excystation occurs in from 

 three to six or more hours. The cause of excystation has been 

 shown by Cropper and Drew (.?), Woodcock and Lapage {3) to be 

 ilue to bacterial ferments, and consequently those amcebse first 

 excysting are found to be those near small masses of bacteria. The 

 first indication of excystation is that one or more minute vacuoles 

 appear in the cytoplasm of the organism, and it retracts somewhat 

 from the cyst wall. Sluggish movement may at this time frequently 

 be observed within the cyst. Finally, the cyst ruptures, appearing 

 to become thinner and thinner usually at one spot, and the con- 

 tained amoebsB gradually emerges, leaving the empty cyst wall 

 behind. On emerging the amoeba appears perfectly normal, and the 

 nucleus well marked. The organism moves away from the empty 

 cyst, but movement is very sluggish. Very shortly it is noticed 

 that the nucleus is becoming very much fainter, and at the same 

 time motion slows down, and the amoeba rounds up and becomes 

 quiescent. It remains in this condition for a time, which may 

 vary from thirty minutes to an hour or more. During such time 

 the nucleus appears to undergo change, although of what nature it 

 has proved impossible to ascertain definitely. Two particles or 

 blepharoplasts are given off from the nucleus, and from these 

 gradually arise two minute flagella ; these increase in length till 

 they are two or three times the length of the amoeba. As soon as 

 the development of the flagella is complete, the amoeba again 

 takes on the ordinary amoeboid form and crawls away with the 



