166 AMOEBOID MOVEMENTS. [BOOK i. 



of the pharyngeal membrane of the frog) becomes injurious ; cold 

 retards. Very dilute alkalis are favourable, acids are injurious. 

 An excess of carbonic acid or an absence of oxygen diminishes or 

 arrests the movements, either temporarily or permanently, according 

 to the length of the exposure. Chloroform or ether in slight doses 

 diminishes or suspends the action temporarily, in excess kills and 

 disorganises the cells. 



Amoeboid Movements. 



95. The white blood corpuscles, as we have said ( 28), are 

 able of themselves to change their form and by repeated changes of 

 form to move from place to place. Such movements of the substance 

 of the corpuscles are called amoeboid, since they closely resemble 

 and appear to be identical in nature with the movements executed 

 by the amoeba and similar organisms. The movement of the 

 endoplasm of the vegetable cell seems also to be of the same 

 kind. 



The amoeba changes its form (and shifts its place) by throwing 

 out projections of its substance, called pseudopodia, which may be 

 blunt and short, broad bulgings as it were, or may be so long and 

 thin as to be mere filaments, or may be of an intermediate 

 character. As we watch the outline of the hyaline ectosarc we 

 may see a pseudopodium beginning by a slight bulging of the 

 outline ; the bulging increases by the neighbouring portions of the 

 ectosarc moving into it, the movement under the microscope 

 reminding one of the flowing of melted glass. As the pseudo- 

 podium grows larger and engages the whole thickness of the 

 ectosarc at the spot, the granules of the endosarc may .be seen 

 streaming into it forming a core of endosarc in the middle of the 

 bulging of ectosarc. The pseudopodium may continue to grow 

 larger and larger at the expense of the rest of the body, and 

 eventually the whole of the amoeba including the nucleus may as 

 it were have passed into the pseudopodium ; the body of the 

 amoeba will now occupy the place of the pseudopodium instead of 

 its old place ; in other words it will in changing its form have also 

 changed its place. 



During all these movements, and during all similar amoeboid 

 movements, the bulk of the organism will, as far as can be 

 ascertained, have remained unchanged ; the throwing out a pseu- 

 dopodium in one direction is accompanied by a corresponding 

 retraction of the body in other directions. If as sometimes happens 

 the organism throws out pseudopodia in various directions at the 

 same time, the main body from which the pseudopodia project is 

 reduced in thickness ; from being a spherical lump for instance it 

 becomes a branched film. The movement is brought about not by 

 increase or decrease of substance but by mere translocation of 

 particles; a particle which at one moment was in one position 



