302 FINE-STRUCTURE OF PROTOPLASMIC DERIVATIVES III 



position of this amino group at the z"'^ C atom corresponds to that of 

 the OH group of the glucose or of the mannose ring (Itschner, 1935). 

 An acetyl residue is linked with the NH2 group; thus, contrary to 

 cellulose, there are here two side chains, viz., an OHCHo-group and 

 a CHgCO-group. 



H N H^ H H 



OH /oh h\h oh /oh nh^ 



H\i_yOH ^\h_^/0H 



CH2OH CH2OH 



Glucose configuration Mannose configuration 



a) Glucosamine 

 NHCOCH3 CH2OH NHCOCH3 CH2OH NHCOCH3 



CH2OH NHCOCH3 CHpOH NHCOCH3 CH2OH 



h) Chain of chit in 

 Fig. 147. Molecular structure of chitin. 



The acetylglucosamine molecules are linked glucosidically and 

 form long chain molecules, each member of which is, according to 

 Meyer and Mark (1930), twisted with respect to its preceding and 

 succeeding neighbour by 180° (Fig. 147 b). X-ray photographs of the 

 sinews of the spiny lobster and of the sporangiophores of Phycomyces 

 show that the crystallographic elementary cell is rhombic, its di- 

 mensions are 9.4 : 10.46 (10.26) : 19.25 A and it contains eight acetyl- 

 glucosamine residues, viz., two to every four main valence chains, 

 which traverse the crystal lattice (Meyer and Pankow, 1935). A 

 different modification of chitin with the crystal lattice 9.32: 10.17: 

 22.15 has been found in Polychaeta and Mollusca. It has been termed 

 i5-chitin, in contrast to the a-chitin of insects, Crustaceae and fungi 

 (Lotmar and Picken, 1950). The fibre period 10.3 A is important, 

 because it corresponds to the length of two pyranose rings and is 

 identical to that of cellulose. This warrants the belief that the glucosan 

 rings, hke the glucose residues of cellulose, are linked together by 

 /5-glucosidic 1-4 bonds (see Fig. 147 b). 



Stihm'icroscopic texture of the chitin frame. Microscopically, the chitin 

 sheath of the Arthropoda and the membranes oi fungi show lamellation 

 and fibrillation, as is known to be the case in the cell walls of cellulose. 

 By analogy, therefore, it may be assumed that fibrillation is realized 



