PROTOPLASM AS A PHYSICAL SYSTEM 65 



down of protoplasmic structures in Protozoa after injury 

 with the microdissection needle.^ 



Facts of this kind show again that the maintenance 

 of a certain characteristic type of structure is an essential 

 part of normal protoplasmic activity. The structure of 

 living protoplasm is not to be conceived as resulting 

 from a combination of static parts like the structure of a 

 machine; it is the product or expression of continual 

 synthetic activity and persists only while metabolism 

 persists; it expresses the constructive activity of metab- 

 olism, very much in the same manner as the structure 

 of a flame or of a fountain expresses the dynamic activity 

 of such a system. If the activity disappears, so also 

 does the characteristic structure or configuration which 

 is maintained by that activity. In this sense, structure 

 in living protoplasm is to be conceived as continually 

 in process of formation; i.e., as an index of the underlying 

 synthetic reactions which, as already seen, are inseparable 

 from the chemical activity of the system during life. 

 The apparently static condition represents in reality a 

 state of balance between construction and disintegration. 



Yet a certain permanent or stable structural consti- 

 tution (at least relatively permanent) has to be assumed, 

 just as in the case of the fountain or candle flame. This 

 is necessary if the dependent processes of chemical trans- 

 formation are to exhibit constant characters. The 

 physical nature of this permanent or persistent structural 

 substratum of living protoplasm has first to be considered. 



^ Kite and Chambers, ^dmce, XXXVI (191 2), 640. Chambers, Trans. 

 Royal Soc. Can., XII (1918), Series 3, 43; Taylor, University of Calif ornia 

 Publications, XIX (1920), 403, cf. pp. 420, 424, 434. Mention has already- 

 been made of Aggazzotti's observations with dark ground illumination on 

 the structural changes produced in blood corpuscles by cytolytic agents . 

 Cf. also Traube and Klein, Biochem. Zeits., CXXX (1922), 477. 



