Immunity in Unicellular Organisms 15 



at once gives the acid colour reaction (Fig. 1 ). Rhumbler 1 has described 



very precisely and with much detail the way in which 



the Amoebae behave when they are incorporating 



filaments of Oscillaria very much longer than 



their own bodies. He has also described the 



digestion that these Algae undergo ; a process 



most characteristic in those cases where a portion 



only of the filament has been taken into the 



interior of the Amoeba and there subjected to Fig x An Amoel)a 



the digestive action. Whilst the free part of treated with neutrai- 



the Oscillaria retains its normal properties and 



appears of a bluish green colour, the ingested portion progressively 



changes colour, assuming first a deep green tint, then becoming 



light yellow, orange yellow, brown and finally reddish brown. 



Simultaneously the cellulose wall of the Alga begins to soften, 



and the cells break up into minute fragments which are soon 



extruded. The food is seldom completely digested and there is 



always an abundant residual material which is thrown out in the 



form of solid excreta. 



Although it is fully recognised that, in the Rhizopods, digestion 

 goes on in a medium distinctly but feebly acid, and that the 

 intervention of some soluble ferment is essential, our ideas on this 

 subject were very vague until the publication of the researches of 

 Mouton 2 , carried out with great care in the Pasteur Institute. In 

 order that he might obtain exact results Mouton made use of 

 cultures of Amoebae grown on agar, in association with the Bacillus 

 coli which served them as food. The bacilli were ingested in large 

 numbers, became enclosed in vacuoles and were digested by a 

 ferment which Mouton was able to obtain in vitro. To that end 

 he collected large numbers of Amoebae, and, after centrifugalising 

 them in water, treated the deposit with glycerine. On adding alcohol [18] 

 he obtained a precipitate readily soluble in water. 



The fluid thus obtained exerted an undoubted digestive action 

 upon albuminoid substances. It readily liquefied gelatine and even 

 attacked, though feebly, albumen coagulated by heat ; flakes of fibrin 

 heated to 58 C. remained unaltered. There was present then, in 

 this fluid derived from Amoebae, a proteolytic diastase of feeble 

 activity. On the other hand, this extract contained neither sucrase, 



1 Arch.f. Entwickelungsmech., Leipzig, 1898, Bd. vn. 



2 Compt. rend. Acad. d. Sci., Paris, 1901, t. cxxxm, p. 244. 



