54 FUNDAMENTALS OF SU BM I C RO S C OPI C MORPHOLOGY I 



corresponds to the general plan of Table VII. The striking fact in this 

 series is that the addition of only a single pair of members to the chain 

 results in such radical changes in the physical properties. It is to be 

 noted that this holds good only for para-substituents in the benzene 

 ring, leading to one-dimensional chain molecules. 



i) p-Azoxybenzene 

 36° 

 cryst. -solid Z^ am. liq. 



o 



2) p-Azoxyphenetolc 



134" il'5 



crvst. -solid 5^ cryst. liq. ^ am. liq. 



^-/ II ^— 



O 



5) p-Azoxy-azobenzene 

 226'' 

 crvst. -solid *^ cryst. liq. ^ dccomp. 



-N=N-< >-N = N^ >-N = N 



6 



4) p-Azoxy-disazobenzene 

 cryst.-solid -^ decomp. 



o 



Fig. 45. Series of chain molecules which aggregate to mesophases (cf. Table VII). 



Myelin for //IS. Cytologists are more famihar with the birefringent 

 semi-liquid tubes, designated as myelin forms because they were ob- 

 served for the first time with myelinated nerves (Fig. 179, p. 362). When 

 water is added to such nerve fibres, adventitious threads issue from 

 their sheath. They bend and curl and finally grow into irregular 

 entanglements. The active substance causing these structures is the 

 lecithin in the myelin sheath, for exactly the same phenomena are 

 observed when water is added to isolated lecithin, especially if this is 

 liable to decompose. Although the myelin forms are particularly strik- 

 ing in organic phosphoric acid compounds, similar tubes emerge 



