ON SOME OTHER FORMS OF CONTRACTILE TISSUE. 121 



led to any satisfactory results, and, as far as we know at present, ciliary 

 action is most affected by changes of temperature and chemical media. 

 Moderate heat quickens the movements, but a rise of temperature beyond a 

 certain limit (about 40 C., in the case of the pharyngeal membrane of the 

 frog) becomes injurious ; cold retards. Very dilute alkalies are favorable, 

 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 dis- 

 organizes the cells. 



Amoeboid Movements. 



91. 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 amceba and similar organisms. 

 The movements 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 pro- 

 jections 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 neighboring portions of the 

 ectosarc moving into it, the movement under the microscope reminding one 

 of the flowing of melted glass. As the pseudopodium 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 amceba 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 pseudopodium in one direction is accom- 

 panied by a corresponding retraction of the body in other directions. If, as 

 sometimes happens, the organism throws out pseudopodia in various direc- 

 tions 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 moves into a new position, several particles thus 

 moving toward the same point cause a bulging at that point, and several 

 particles moving away from the same point cause a retraction at that point ; 

 but no two particles get nearer to each other so as to occupy together less 

 space and thus lead to condensation of substance, or get further from each 

 other so as to occupy more space and thus lead to increase of bulk. 



In this respect, in that there is no change of bulk but only a shifting of 

 particles in their relative position to each other, the amoeboid movement 

 resembles a muscular contraction ; but in other respects the two kinds of 

 movement seem different, and the question arises, have we the right to speak 



