4 PKOTOPLASM. 



the others. In another sense it is not homogeneous; for we 

 know that the amoeba receives into its substance material as food, 

 and that this food or part of it remains lodged in the body until 

 it is made use of and built up into the living substance of the 

 body ; and each piece of the living substance of the body must 

 have in or near it some of the material which it is about to build 

 up into itself. Further, we know that the amoeba gives out waste 

 matters, such as carbonic acid and other substances ; and each piece 

 of the amoeba must contain some of these waste matters about to 

 be, but not yet, discharged from the piece. Each piece of the 

 amoeba will therefore contain these three things : the actual living 

 substance, the food about to become living substance, and the 

 waste matters which have ceased to be living substance. 



Moreover, we have reasons to think that the living substance 

 does not break down into the waste matters which leave the body 

 at a single bound, but that there are stages in the downward 

 progress between the one and the other. Similarly, though our 

 knowledge on this point is less sure, we have reason to think 

 that the food is not incorporated into the living substance at a 

 single step, but that there are stages in the upward progress 

 from the dead food to the living substance. Each piece of the 

 body of the amoeba will therefore contain substances represent- 

 ing various stages of becoming living, and of ceasing to be 

 living, as well as the living substance itself. And we may 

 safely make this statement though we are quite unable to draw 

 the line where the dead food on its way up becomes living, or the 

 living substance on its way down becomes dead. 



§ 5. Nor is it necessary for our present purpose to be able to 

 point out under the microscope, or to describe from a histological 

 point of view, the parts which are living and the parts which are- 

 dead food or dead waste. The body of the amoeba is frequently 

 spoken of as consisting of ' protoplasm.' The name was originally 

 given to the matter forming the primordial utricle of the vegetable 

 cell as distinguished from the cell wall on the one hand, and from 

 the fluid contents of the cell or cell sap on the other, and also 

 we may add from the nucleus. It has since been applied very 

 generally to such parts of animal bodies as resemble, in their 

 general features, the primordial utricle. Thus the body of a white 

 blood corpuscle, or of a gland cell, or of a nerve cell, is said to 

 consist of protoplasm. Such parts of animal bodies as do not in 

 their general features resemble the matter of the primordial utricle 

 are not called protoplasm, or, if they at some earlier stage did bear 

 such resemblance, but no longer do so, are sometimes, as in the case 

 of the substance of a muscular fibre, called ' differentiated proto- 

 plasm.' Protoplasm in this sense sometimes appears, as in the 

 outer part of most amoebae, as a mass of glassy-looking material, 

 either continuous or interrupted by more or less spherical spaces 

 or vacuoles filled with fluid, sometimes as in a gland cell as a more 



