422 THE POPULAR SCIENCE MONTHLY, 



THE IMPOET OF PKOTOPLASM.^ 



By MICHAEL TOSTEE, M. D., F. E. S. 



AMONG the simpler organisms known to biologists, perhaps the 

 most simple as well as the most common is that which lias re- 

 ceived the name of Amoeba. There are many varieties of amoeba, 

 and probably many of the forms which have been described ai-e, in 

 reality, merely amoebiform phases in the lives of certain animals or 

 plants ; but they all possess the same general characters. Closely 

 resembling the white corpuscles of vertebrate blood, they are wholly 

 or almost wholly composed of iindiflerentiated protoplasm, in the 

 midst of which lies a nucleus, though this is sometimes absent. In 

 many a distinction may be observed between a more solid external 

 layer, or ectosarc^ and a more fluid granular interior, or endosare ; but 

 in others even this primary differentiation is wanting. By means of a 

 continually occurring flux of its protoplasmic substance, the amoeba 

 is enabled from moment to moment not only to change its foim, but 

 also to shift its position. By flowing round the substances which it 

 meets, it, in a way, swallows them; and, having digested and absorbed 

 such parts as are suitable for food, ejects or rather flows away from 

 the useless remnants. It thus lives, moves, eats, grows, and after a 

 time dies, having been during its whole life hardly anything more 

 than a minute lump of protoplasm. Hence to the physiologist it is 

 of the greatest interest, since in its life the problems of physiology 

 are reduced to their simplest forms. 



Now, the study of an amoeba, with the helja of knowledge gained 

 by the examination of more complex bodies, enables us to state that 

 the undifierentiated protoplasm, of which its body is so largely com- 

 posed possesses certain fundamental vital properties : 



1. It IS CONTRACTILE. There can be little doubt that the changes 

 in the protoplasm of an amoeba, which bring about its peculiar " amoe- 

 boid " movements, are identical in their fundamental nature with those 

 which, occurring in a muscle, cause a contraction ; a muscular con- 

 traction is essentially a regular, an amoeboid movement an irregular 

 flow of protoplasm. The body of the amoeba may therefore be said 

 to be contractile. 



2. It is irritable and automatic. "When any disturbance, such as 

 contact with a foreign body, is brought to bear n the amoeba at rest, 

 movements result. These are not passive movements, the effects of 

 the push or pull of the disturbing body, and therefore proportionate 

 to the force employed to cause them, but active manifestations of the 

 contractility of the protoplasm ; that is to say, the disturbing cause or 



' From the introduction to M. Foster's *' Text-Book of Fhysiology." 



