104 The Structure of Protoplasm 



the internal kinoplasm is a normal and presumably functional 

 organization. Yet the tendency of cytoplasmic surface films in 

 general to form these myelin-like outgrowths on both their surfaces, 

 has significance with respect to the composition and molecular 

 structure of both the films and the fibrils. 



At this point attention may be drawn to Figure 1, which shows 

 diagrammatically the supposed position and relationship of the 

 differentiations described. 



MOLECULAR STRUCTURE 



On the basis of physical properties and probable structure, the 

 cytoplasmic differentiations fall into two groups. The plasmasol and 

 plasmagel, being reciprocally transformable, are merely different 

 physical states of one substance. The same relation seems to hold 

 between the films and kinoplasm. But the two pairs show no sign 

 of being interchangeable, and what is more significant, they ex- 

 hibit fundamentally different properties. Those of the sol-gel 

 region, the endoplasm, include elasticity, thixotropy, stream bi- 

 refringence, etc., which, as shown by the previous speaker, point to 

 elongated protein units as the building stones. On the other hand, 

 the properties of the film-kinoplasm complex are prominently 

 lipoidal, though no doubt proteins also enter into its composition. 

 Incidentally, while the film substance occupies much the lesser part 

 of the protoplast, yet (if such a distinction can be made) it is the 

 more essential part, being capable of preserving an independent 

 existence for a time, which the endoplasm is unable to do. 



Let us see what these lipoidal properties are. Already men- 

 tioned is the tendency to myelin formation, a phenomenon confined 

 to a limited group of substances including phosphatides, cerebro- 

 cides and trioleates — all ingredients of protoplasm. It depends on 

 the assumption of paracrystalline structure, consisting of parallel 

 sheets of orientated molecules with the principal optical axis and 

 longer diameter of the molecules at right angles to the plane of 

 layering. The type of birefringence which results from this form 

 of structure tends to disappear with a high degree of hydration and 

 reappear on dehydration. Accordingly, it is significant that such 

 double refraction develops in the hyaline layer on the amoebocytes 

 of various invertebrates when partially dehydrated (Faure-Fremiet, 

 see Schmidt). Masses of myelin-forming material which, under 

 certain conditions, accumulate on the lining of the plant vacuole. 



