34 Elementary Biology. 



immediately produces a general contraction and drawing 

 in of all pseudopodia, amounting, if the shock be a strong 

 one, to actual paralysis and death. 



Motion, however, seems in many cases to be produced 

 independently of external stimulus, and to arise as a conse- 

 quence of some internal chemical changes taking place, not, 

 as in the previous case, in response to stimuli, but automa- 

 tically. Protoplasm is said, therefore, to possess automatism. 



Other stimuli than those mentioned produce local irri- 

 tability and motion of a peculiar kind. Contact with solid 

 particles produces a movement of the neighbouring proto- 

 plasm, and results in the engulfing of the particles into the 

 viscous mass by the protrusion of pseudopodia which sur- 

 round and inclose them. The food-particles thus inclosed 

 undergo certain changes in the interior of the cell during a 

 species of circulation which they experience in its mass 

 changes which result in the absorption, alteration, and 

 preparation of the particles into compounds from which 

 new protoplasm is integrated changes which are no doubt 

 brought about by the chemical action of certain substances 

 present in, and formed from, trie protoplasm. In conse- 

 quence of this power of absorbing or ingesting food particles 

 the protoplasm is said to possess the power of assimilation. 

 These primary changes are followed by others of a more 

 complicated nature, in virtue of which new protoplasm is in- 

 tegrated or built up. It will be convenient to designate all 

 chemical changes taking place in the organism as metabolic 

 changes ; changes concerned in the building up of proto- 

 plasm will therefore constitute constructive metabolism or 

 anabolism ; whilst the changes which take place in the 

 decomposition of protoplasm may be termed collectively 

 destructive metabolism or katabolism. The products of 

 anabolism and katabolism will therefore be naturally termed 

 anastates and katastates respectively. 



The destructive changes to which protoplasm, when 

 formed, becomes at once liable, result in the production of 



