1907.] Chitin by its Physical Constants. 479 



I can only state that the substance has, like the integument of other 

 Lepidopteran pupse, the physical properties of chitin, and that I have 

 obtained evidence of the presence of sugar in it after treatment with 

 90-per-cent. sulphuric acid at a temperature of 40° C. for 24 hours. The 

 sugar was detected by Trommer's test, as in the other cases mentioned.* 

 The molluscan radula I have studied from this point of view by this method 

 chiefly in the case of the periwinkle, Littorina littorea, the limpet, Patella 

 vulgala, and the whelk, Buccinum undatum. The radula of Patella, as I have 

 shown elsewhere,f contains silica and iron in considerable quantities. 

 To cleanse it we must, therefore, treat it for some time (24 hours) with 

 strong hydrofluoric acid. A control experiment showed that the specific 

 gravity of chitin from the integument of Astacus was unaltered by this 

 treatment. After washing out the hydrofluoric acid the usual method of 

 preparing chitin was used. The radulse still retain a faint yellow colour 

 after this treatment ; they were placed in chlorine water, when they became 

 colourless and somewhat transparent. They were cut into short lengths, 

 and these were found to form a neat zone in the diffusion column at a level 

 corresponding to a specific gravity 1*405 to 1*407. Littorina radulse gave 

 a closely similar result. In the case of Littorina I used the confirmatory 

 test, and obtained reduction of copper salts by Trommer's method. 



Buccinum radulse differ from the others which were measured in that 

 they form a broad irregular zone in a diffusion column. The extreme tips 

 of the radulae, taken from the radular sac, however, give a uniform specific 

 gravity of 1*404. The remainder of the radulse form a band extending from 

 1*400 to 1*411, or even lower. It is noticeable that the pieces in this band 

 for the most part hang with their greater length vertical, and the oldest 

 end of each length is lowermost. It, therefore, seems possible that some 

 second resistent substance, in addition to chitin, is present in this case in 

 increasing quantities as we pass forwards from the radular sac. If this 

 is the correct interpretation of the facts, it is interesting in connection with 

 the occurrence of free sulphuric acid in the salivary glands of Buccinum, and 

 it is not surprising that an organ used to bore holes in shells with the 

 aid of sulphuric acid should need to be specially resistent. For some time 

 I fancied that the irregularities in the specific gravity of this radula might 

 be due to small particles of sand caught between the bases of the teeth and 

 the basal membrane. But the specific gravity of the teeth, when isolated 



*' Since this was written, von Fiirth and Russo have shown by chemical methods that 

 the integuments of Lepidopteran pupse consist of ordinary chitin, 'Beitr. z. chem. 

 Physiol, u. Pathol.,' vol. 8, 1906. 



t 'Quart. Journ. Micr. Sci.,' 1907, vol. 5J, pp. 115—136. 



