CARBOHYDRATES, CHITIN AND CUTIN 



303 



in the submicroscopic region. The interfibrillar spaces in crustacea 

 are filled partly with mineral substances, especially with calcium 

 carbonate, while the membranes of fungi are encrusted with sub- 

 stances rather of a carbohydrate or pectinous nature (which can be 

 extracted by boiling for several hours with a ten per cent, solution of 

 caustic potash). 



r; 



b?) 



e) 



Fig. 148. Types of submicroscopic texture with chitin as the frame substance, a) Crab 

 sinew: fibrous texture, b) Interior of lobster shell: submicroscopic lamellar texture, with 

 direction of fibrillae changing from lamella to lamella (i, 2, 3, 4, etc.); bj) cross-section, 

 bg) plan, /r) Eggshell of Ascaris: foliate texture (Schmidt, 1936b). d) Conidiophores of 

 Aspergillus: fibroid texture (Frey, 1927a). e) Conidiophores of Phycomyces: spiral texture 



(OoRT and Roelofsen, 1932). 



As with cellulose, the orientation of the rods of the frame is 

 demonstrable by optical means, since the larger axis of the index 

 ellipse of sections immersed in water or gh^cerol runs parallel to the 

 submicroscopic chitin rodlets. This method reveals the same potential 

 orientation as that actualized in cellulosic cell walls (Fig. 148). 



Chitinous tendons of crabs, lobsters, beetles, etc. are of an un- 

 mistakable fibrous texture. Of all chitinous objects, therefore, they 

 produce the most richly pointed X-ray diagrams and are thus the most 

 informative as to the lattice structure of chitin. Optically, the fibrous 

 texture is disclosed by the fact that the refractive power is considerably 

 more pronounced parallel to the axis of the tendon than perpendicular 

 to it, while something like isotropy prevails in the cross-sections of 

 the tendon. This fibrous texture is to be inferred, not only from the 

 birefringence, but also from the anisotropy of the absorption of light. 

 Iodine-zinc chloride solution and Congo red stain decalcified and 



