1907.] Chitin by its Physical Constants. 47 f 



added acid. The solution in hydrochloric acid, when kept at a temperature 

 of less than 0° C, is thus seen to be not unstable. The precipitate, which 

 was floceulent, was washed by decantation until an acid reaction was no 

 longer obtained ; it was then boiled in alcohol and ether. Placed in a 

 specific gravity column, it formed a broad zone, extending from 1*380 to 

 1*390. Some of the precipitate was then dried at a low temperature 

 (40° to 60° C). It formed a thin film on the evaporating dish, which was 

 scraped off with a scalpel, and then formed a white powder. This powder 

 had a specific gravity 1*398, and this, I conclude, is the specific gravity of 

 chitin. If dried too rapidly at a higher temperature than 60°, the precipitate 

 flakes off the dish and its specific gravity is no longer uniform. 



The substances of unknown chemical composition which I have examined 

 by this method are Lumbricus bristles, the organic portion of the molluscan 

 radula, the pupal skin of Pieris, and of some other Lepidoptera stated by 

 Griffiths to be " pupin." I had hoped to deal also with the skeletal 

 substance of the branchial bars of Amphioxus, which are stated to be 

 insoluble in alkalis, but I could obtain no residue after boiling the pharynx, 

 even in weak caustic potash. An account of the specific gravity of the 

 organic portion of the shell of Sepia, in which chitin has been found by 

 Krukenberg, is also given below. Lumbricus chaetse were isolated in the 

 following manner: — The worm was slit up along the mid-dorsal line and 

 the alimentary canal and its contents removed. The remaining body wall 

 was then washed in a current of water to remove any matters which might 

 have escaped in the process of removal of the gut. The contents of the 

 gut are troublesome unless removed at once. The worms thus far cleaned 

 are now treated with 10-per-cent. hydrochloric acid, and then boiled in 

 potash as usual in the preparation of chitin. If after prolonged treatment 

 with potash any matter other than chaetse remains undissolved, this is most 

 readily got rid of at a later stage of the cleansing process (after extraction 

 in alcohol) by separation in a diffusion column, say of chloroform and alcohol. 

 The bristles will float on the chloroform, the insoluble dirt (presumably 

 sand, undigested wood fibres, and cellulose, set free in removing the 

 alimentary canal) sinks to the bottom. The bristles can then be removed 

 with a pipette and extracted in ether. In this way a considerable quantity 

 of chsetse can be collected with very little trouble. They form a neat zone 

 in a diffusion column at a level corresponding to a specific gravity 1*392. 

 They are doubly refracting. I have measured one index only, it lay between 

 1-557 and 1*550. I conclude, therefore, that the chsetse of Lumbricus 

 contain chitin. This is in agreement with the results obtained by Goodrich.* 

 * ' Quart Journ. Micr. Sci./ 1897, vol. 39, " Notes on Oligochsetes." 



2 M 2 



