INTRODUCTORY. 



AMONG the simpler organisms known to Biologists, perhaps the 

 most simple as well as the most common is that which has received 

 the name of Amoeba. There are many varieties of Amoeba, and 

 probably many of the forms which have been described are, 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 undifferentiated 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 endosarc; 

 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 form but also to shift its position. By flowing round the sub- 

 stances 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 help of knowledge 

 gained by the examination of more complex bodies, enables us to 

 state that the undifferentiated protoplasm of which its body is so 

 largely composed exhibits certain fundamental phenomena which 

 we may speak of as ' vital.' 



F. 1 



