HANDBOOK OF PHYSIOLOGY. 



1. TJie power of spontaneous movement. When an amoeba is observed 

 with a sufficiently high power of the microscope, it is found to consist 

 of an irregular mass of protoplasm distinguished into an outer dense 



layer and an inner more fluid mass. If 

 watched for a minute or two an irregular 

 projection or pseudopodium is seen to be 

 gradually thrust out from the main body 

 and retracted: a second mass is then pro- 

 truded in another direction, and gradu- 

 ally the whole protoplasmic substance 

 is, as it were, drawn into it. The Amoeba 

 thus comes to occupy a new position, 



and when this is repeated several times we have locomotion in a definite 

 direction, together with a continual change of form. These movements, 

 when observed in other cells, such as the colorless blood- corpuscles of 



FIG. 1. Amoebae. 



FIG. 2 Human colorless blood-corpuscle, showing its successive changes of outline within ten 

 minutes when kept moist on a warm stage. (Schofield.) 



higher animals (Fig. 2), in the branched cornea cells of the frog and 

 elsewhere, are hence termed amwboid. 



Other illustrations of amoeboid movement. The remarkable motions 

 of pigment-granules observed in the branched pigment-cells of the f rog's 

 skin by Lister are probably due to amoeboid movement. These granules 

 are seen at one time distributed uniformly through the body and 

 branched processes of the cell, while under the action of various stimuli 

 (e.g., light and electricity) they collect in the central mass, leaving the 

 branches quite colorless. 



Ciliary action must be regarded as only a special variety of the gen- 

 eral motion with which all protoplasm is endowed. 



The grounds for this view are the following : In the case of the 

 Infusoria, which move by the vibration of cilia (microscopic hair-like 

 processes projecting from the surface of their bodies) it has been proved 

 that these are simply processes of their protoplasm protruding through 

 pores of the investing membrane, like the^oars of a galley, or the head 

 and legs of a tortoise from its shell: certain reagents cause them to be 

 partially retracted. Moreover, in some cases cilia have been observed 

 to develop from, and in others to be transformed into, amoeboid pro- 

 cesses. 



In the hairs of the stinging-nettle and Tradescantia and the cells of 

 Vallisneria and Chara, the movement of protoplasm can be marked by 

 the movement of the granules nearly always imbedded in it. For 

 example, if part of a hair of Tradescantia (Fig. 3) be viewed under a high 

 magnifying power, streams of protoplasm containing crowds of granules, 

 hurrying along, like the foot passengers in a busy street, are seen flow- 



