470 INTKA-CELLULAR DIGESTION. [BOOK II. 



the reader will now be drawn. When an Amceba is observed in 

 active movement, it is seen to be progressing in one direction, "so 

 that a fairly constant hind end may be distinguished, and in this 

 organism it is the hind end which most actively ingests. The 

 ectosarc is drawn like a funnel round the prey, and the opening 

 which corresponds to the mouth of the funnel is ex-centrically closed. 

 In the case of quiescent solid matter, such as starch grains or Torulse, 

 but little fluid is included ; when, however, an actively moving prey 

 is dealt with, an area of water not inconsiderable surrounds it. The 

 ectosarc of two enclosing pseudopodia first fuses distally of the 

 object and leaves a space in which movement goes on a space only 

 gradually reduced, and never done away with by complete inclusion." 

 Some of the lateral pseudopodia of Amoeba proteus may exercise 

 prehensile function, but ingestion at the most anterior and most 

 actively moving part never occurs. The length of time occupied by 

 this act of ingestion varies greatly in different protozoa, but in 

 Amoeba is comparatively short though variable. ' Contact may be 

 established and broken many times with no result, but determinate 

 ingestion is a matter of minutes rather than hours.' In studying the 

 digestive processes of the Amoeba and Actinosphserium, Miss Green- 

 wood supplied the creatures with various kinds of solid particles, viz. 

 with (a) starch grains and cellulose ; (6) fat globules (milk) ; (c) 

 organisms in which a protoplasmic body is surrounded by a cellulose 

 wall; (d) unshielded proteid chiefly in the form of small animals 

 without tests; (e) presumedly innutritions matter, such as litmus. 

 Of these substances, the following appeared useless to the Amoeba 

 for purposes of nutrition : the fat, the pure carbohydrates and the 

 litmus. If we take, as an example of these, starch grains, we find 

 that after a stay of some days they are ejected unaltered in form, in 

 size, and in their reaction towards iodine. It was mentioned that 

 when solid bodies are ingested by an Amceba, after their enclosure a 

 space (vacuole) containing some water is seen surrounding them. 

 If the body be one which the creature cannot digest, this water soon 

 disappears, and is not replaced by any newly secreted liquid, i.e. the 

 vacuole ceases to exist. When, however, either naked or ' shielded ' 

 protoplasmic food is ingested by the Amoeba, its presence seems to 

 act as a stimulus to the secretion of a liquid which surrounds the 

 matter to be acted upon, which may then be said to occupy ' a 

 vacuole of digestion.' 



That the liquid which is poured out into a digestive vacuole 

 must actually exert a chemical action upon protoplasmic bodies 

 might be held to be proved by the fact that the latter may be 

 actually seen to disintegrate as it surrounds them. A conclusive 

 proof is, however, afforded by the digestion of organisms possessed of 

 a cellulose wall ; the latter is neither dissolved nor perforated, and 

 yet its contents are digested, a result which is only explicable on the 

 supposition that an active digestive liquid has been able to diffuse 

 through the cellular wall and then exert its solvent action. 



