l86 FINE-STRUCTURE OF PROTOPLASM II 



valency bonds would be fundamentally different from that of a gel 

 whose chain molecules are connected by homopolar valency bonds. 

 While this criticism touches the theory of junctions in the molecular 

 range, Lehmann and Biss (1949) raise objections to reticula, whose 

 strands have diameters lying on the borderline between submicro- 

 scopic and microscopic dimensions. They contend that the theory 

 considers only molecular or micellar frameworks and neglects gel 

 structures with coarser strands, such as the beaded fibrils found in the 

 Tuhifex egg. This argument disregards the basic principle of the theory 

 of junctions, which has been advanced in opposition to the view that 

 the cytoplasm is a liquid, because to my mind its capacity to gelate 

 is a vital necessity. Since it is not known which forces cause the cyto- 

 plasm to set, in 1938 I introduced the notion of junctions, a term which 

 does not imply any special type of binding forces. If the possibilities 

 of junctions in the amicroscopic range have been more extensively 

 described, it is only because very little is known of other types of 

 junctions, such as long-range forces. But this by no means implies 

 that only molecular gels are involved. On the contrary, every possible 

 type of gel must be taken into account; and it is the task of submicro- 

 scopic cytology to establish the nature of the junctions involved. 



e. Protoplasmic Flow and Cell Polarity 



Protoplasmic flow. The touchstone for the correctness of any theory 

 of protoplasmic structure is a self-consistent explanation of proto- 

 plasmic flow. For this reason the latest results of the investigations 

 "on this important phenomenon of life will be briefly discussed. 



The cells and plasmodia, in which it has so far been possible to 

 analyze flow in detail, all show a sol-like liquid inner protoplasm 

 (plasma sol) and a gel-like, solidified outer skin (plasma gel) (Lewis, 

 1942; Marsland, 1942; Moyer, 1942; ScARTH, 1 942; Seifriz, 1942, 

 1943; Andresen, 1942). The difference in colloid state between the 

 two types of protoplasm is demonstrated by the Brownian movement 

 of microscopic granules. These are in lively movement in the bulk 

 protoplasm (endoplasm) where the viscosity is low, but in the solid 

 protoplasmic skin (ectoplasm), they have the appearance of being 

 frozen. According to Gold acre and Lorch (1950), the protein mole- 

 cules are in a folded state in the liquid endoplasm and in an unfolded 

 (denatured) state in the gelated ectoplasm. 



