84 



MANUAL OF PHYSIOLOGY. 



FlG. 35. 



taking place at any given part of the cell body are rapidly dis- 

 tributed over the entire mass of the protoplasm. 



If there be no definite cell wall as in naked vegetable spores, 

 and amoeboid forms of animal life to restrict or direct the cur- 

 rent of protoplasm, it flows out in various directions in bud-like 

 processes, which appear at various parts of the protoplasmic mass, 

 so as to cause a constant change in the form of the cell. These 

 outstretched processes sometimes flow together and unite com- 

 pletely, often inclosing some of the medium in which the creature 

 is suspended, or catching some foreign particle floating near them. 

 The flowing out of these pseudopodia commonly takes place for 

 some little time persistently from one side of the cell ; and the 



body of the cell, as it were, has to 

 follow the protrusion of the pro- 

 cesses in such a manner that in a 

 little time definite change in posi- 

 tion or movement in a certain di- 

 rection occurs ; thus the unit of 

 protoplasm may be said to per- 

 form definite progress of locomo- 

 tion. All these movements may 

 be seen in the white blood cor- 

 puscles of a cold-blooded animal, 

 such as a frog, and still more 

 easily in the unicellular being 

 known as amceba. 



Various influences may be 



seen to affect the rate of movements, and probably influence 

 at the same time the other activities of the protoplasm. Fore- 

 most among these must be named : (1) Temperature. If a pro- 

 toplasmic unit which is observed to be motile be gently warmed, 

 the movements become more and more active as the temperature 

 is raised, until at a certain point, about 35-42 C., a spasm 

 occurs, resulting in the withdrawal of the pseudopodia; soon 

 after which the cell assumes a spherical shape. If the heat be 

 carefully abstracted by the gentle and short application of cold, 

 the protoplasm may be made to recover and again commence its 



An amoeba figured at two different 

 moments during movement, showing a 

 clear outer layer and a more granular 

 central portion. (ri) Nucleus; (i) In- 

 gested food. (Gegenbaur.) 



