86 BIOLOGICAL LECTURES. 



respiration by wandering toward the dorsal epidermis. Before 

 the excretophores are loaded with waste products the ordinary 

 supply of oxygen is sufficient for their wants, and they only 

 show the above tendency after this ordinary supply is no longer 

 sufficient. 



A third question which we have to answer is: Why do the 

 excretophores disintegrate when they reach the skin ? 



We have here to distinguish two successive stages of disinte- 

 gration, — the mechanical and the chemical. The mechanical 

 disintegration takes place before the excretophores have reached 

 the epidermis; the chemical disintegration sets in as soon as 

 the excretophores have reached the seat of respiration. 



We know that during the creeping motion of an Amoeba, or 

 a leucocyte, two mechanical forces act upon the active mass, — 

 the cohesion of the body itself and the adhesion to the sub- 

 stratum. The motion of Amoeba has two phases, active creep- 

 ing or change of form, and passive reconstruction of form, the 

 progression depending upon these two factors. 



I am far from endeavoring to enter into any speculation as 

 to the causes of amoeboid motion, and will only try to show 

 that the two balancing principles of adhesion and cohesion are 

 the cause of the progression and mechanical disintegration of 

 the excretophores. 



If an Amoeba creeps, it first sends out a pseudopodium, 

 which adheres firmly to the substratum, and the principle of 

 cohesion in fluids immediately sets in to reconstruct the original 

 form by making the rest of the protoplasm flow after the pseu- 

 dopodium. The vortical motion depends entirely upon the 

 reciprocal balance between adhesion and cohesion. If we let 

 Amoeba creep upon a substratum, or in a medium where adhe- 

 sion will overbalance cohesion, the result will consist of a 

 separation of the pseudopodium from the main body, that is, 

 of mechanical disintegration. The moving impetus is given, 

 and of a definite strength, whereas cohesion is not sufficiently 

 powerful to let the body follow as quickly as the pseudopodium 

 advances. Experiments have been made in this line by causing 

 Amoeba to creep in gelatine and the result was a mechanical 

 dis'ntegration of the animal. 



