20 THE CELL 



and reconnaissances. Mobility of the component parts is in fact an 

 indispensable condition of efficiency on the part of the entire army, 

 which to llif eye of an uninitiated onlooker seems to flow like a mighty 

 si ream over the countryside. Similarly protoplasm presents the appear- 

 ance of a semi-liquid, structureless substance, whereas actually this 

 outward semblance of liquidity merely expresses that very mobile 

 condition of the constituent particles which is essential to the continu- 

 ance of the highly intricate vital activity. This internal mobility 

 entails, it is true, certain physical consequences; it is, in other words, 

 accompanied by phenomena which appear also in connection with life- 

 less liquids and emulsions. But these purely physical phenomena 

 have no immediate connection with what may be termed the vital 

 aspect of protoplasmic structure and activity. 6 



It may be remarked that the consistency of the protoplasm is not 

 necessarily the same in every part of a given cell, while one and the 

 same portion of a protoplast may vary in consistency at different times; 

 certain components of the protoplast may temporarily or permanently 

 display a relatively solid character, doubtless in relation to the special 

 functions with which these components are entrusted. 



Naturally many attempts have been made to demonstrate that 

 protoplasm is possessed of a visible structure and differentiation. 

 Among the various theories which have been propounded in this 

 connection Butschli's hypothesis of the universal " foam structure " of 

 protoplasm perhaps rests upon the widest basis of fact. There can 

 indeed be no doubt that a delicate alveolar structure of the protoplasm 

 is widely distributed as regards both animal and vegetable cells, and 

 that this structure plays an important part in connection with various 

 functions of the living substance. On the other hand, it cannot be 

 denied that under certain conditions fibrillar structures also appear 

 within the protoplasm. In many cases the fibrillar appearance in 

 reality corresponds to the outlines of a reticulum which has been 

 produced by the partial collapse of the walls of greatly elongated 

 alveoli : in other instances, however, delicate fibrils actually seem to 

 be differentiated within the protoplasm composing the alveolar walls. 

 Slrasburgor accordingly discriminates between "alveolar" and "filar" 

 plasma, at the same time attributing different functions to these two 

 varieties of protoplasm. The former is termed trophoplasm by Stras- 

 I auger, because it seems to be chiefly concerned with the process of 

 nutrition : the latter is supposed to be active mainly in connection 

 with developmental changes, and is therefore termed kinoplasm. 

 Further investigation is required in order to decide how far this 

 dist inction is justified. 



The chemical constitution of the living substance is quite in keeping 



