I THE PROTOZOA 7 



The Nature By chemical analysis, the constituent elements 

 of Proto- of which this protoplasm is formed can be 

 plasm, determined. It consists of carbon, hydrogen, 

 oxygen, nitrogen, and sulphur, with minute traces of phos- 

 phorus and other elements, but by no method of chemical 

 synthesis, yet known to us, can we cause these elements to 

 reunite to form living protoplasm once more. The secret of 

 life is hidden from us.^ 



Such living protoplasm, however, exhibits certain definite 

 phenomena, which, though we know not their ultimate origin, 

 we learn to recognise as characteristic of life — the phenomena, 

 namely, of irritability, or power to respond to stimuli, of 

 movement, of absorption and digestion of food, of respiration 

 and excretion of waste matter, and, finally, of growth and 

 reproduction. Even such a simple organism as Amoeba ex- 

 hibits these vital phenomena, though in their simplest forms. 



Locomotion ^^ Amoeba, movement consists merely of the 

 streaming of the protoplasm towards one point, 

 so forming a long process, the rest of the protoplasm gradually 

 flowing after it in the same direction ; each such process is 

 known as a " pseudopodium," or "false-foot" ; in this manner 

 the Amoeba can make its way over the mud and debris 

 amongst which it lives. 



The absorption of food takes place by a 

 modification of the process of motion. Two 

 pseudopodia are formed by the streaming outwards of the 

 protoplasm, and these gradually surround the object desired, 

 which consists usually of some very minute animal or 

 vegetable organism. The processes fuse round the food 

 particle, so that it is actually engulfed in the protoplasm, 

 together with a little drop of water forming a "food vacuole." 

 The soft, soluble parts of the food are then dissolved, probably 

 by some digestive juice secreted by the protoplasm, and so 

 the food is rendered capable of absorption and assimilation, 

 new protoplasm being built up from it. Undigested solid 

 portions of food are got rid of by the simple flowing of the 

 protoplasm away from the matter to be rejected, just the 

 reverse process from that by which it was at first engulfed. 



' For account of experiments to illustrate the nature of protoplasm, refer 

 to Investigations on Microscopic Forms and on Protoplasm, by 0. Biitsclili, 

 English translation by E. A. Minchin (A. and C. Black, London, 1894), 



