Cited by M. Greenwood and E.R. Saunders, 'On the Rôle of Acid in Protozoan Digestion', Journal of Physiology 16 (5-6) (1894), pp. 441-467.
Description:

'The possibility that the substance of animal cells may give rise within itself to accumulations of acid fluid, even when these cells are not highly differentiated, has been considered indeed by many earlier writers, and their statements have gained a degree of familiarity by repetition. But if we except a paper by M. Metchnikoff [note: 'E. Metchnikoff. Annales de l'Inst. Past. 1889, p. 25.'], which contains a discussion of the reaction of plasmodia to ingested litmus, we find that the records which bear on this question are often incidental and unsupported by the details of experiment. Among these the following statement made by De Bary [note: 'E. de Bary. [sic] Pilze, Mycet. und Bact. p. 487.'], and now almost classical, must be placed, - "As to the changes which ingested bodies may undergo in the interior of a plasmodium, this one observation is established, that, in the case of Didymium serpula, carmine is dissolved." No detailed account of the observation is given nor is there any attempt to harmonize it with the statement which succeeds immediately, that carmine is ingested rarely and never dissolved by the nearly allied Didymium libertianum. It seems clear that De Bary is concerned rather with the fact that solid bodies are ingested by the Mycetozoa than with the intracellular surroundings of ingesta.' (441)

 

'Since the days when De Bary and Engelmann wrote, observations have been made by one of us on the digestive process in Amoeba and Actinosphaerium. These observations sought to establish the constant association of a fluid medium with the manifestation of proteolytic activity in Protozoa, and secondarily, the reaction of this medium.' (442)

 

'Carmine grains ingested alone are unchanged by Carchesiurn or by the plasmodia we have used; ingested with nutritious matter they are equally unchanged, but they adhere to the lessening remnant of food throughout digestion. When ingesta stained with carmine as a preliminary to enclosure are watched, the digestive vacuole is seen to be colourless at first but soon afterwards is clearly red. This colour which belongs wholly to the solution of stained matter seems to us comparable to the red colour set free in peptic digestion of carmine-stained fibrin [note: 'Cp. P. Grützner, Neue unter. ü. d. Bild. u. Auss. d. Peps. (Breslau, 1875); and J. N. Langley, This Journal, Vol. III. 1880.']; it is in fact distinctly different from the "lake" colour of carmine in alkaline solution. We have examined these relations carefully and repeatedly because of the use made of carmine by De Bary in the experiments quoted at the beginning of this paper. It will be remembered that he speaks of the solution of carmine within the plasmodium of one mycetozoan, while a nearly allied form ingested little and dissolved none. Many succeeding writers have quoted De Bary's statement; Pfeffer [note: 'Op. cit.'] discusses it in the papers to which we have referred above, and we gather that he is inclined to explain the result by postulating the possibility of locally variable response to like stimuli from any area of a plasmodium. By such an hypothesis solution of carinine and inaction on carmine are demonstrable, conceivably, on neighbouring ingesta. No instance of such extreme local dissimilarity is adduced, but stating that Chondriodermoa difforme [note: 'The Didymium Libertianum of De Bary'] ingests carmine abundantly (in this form De Bary found that there was practically no ingestion) Pfeffer notes that in most cases the grains remained unaltered, while exceptionally, a vacuole, coloured red by solution, is formed. We think that the possibilities of variable reaction are somewhat overestimated by Pfeffer; for us, as formulated by him, they transcend experience. And bearing in mind how actually meagre is this classical statement, how partial the support which it has gained in later years [note: 'Cp. A. Lister. Journ. Linn. Soc. Vol. L. The ingestion of carmine grains by swarm cells of Mycetozoa is described without subsequent digestion (p. 439.)'], and the entire absence of solution of carmine grains which is noticeable constantly in our experiments, we think it a more probable hypothesis that solution (when it occurred) was due rather to some accidental constituent of a vacuole ingested from without than to secretion poured from the surrounding cell substance.' (457-458)