1868.] Additions to the knowledge of Silk. 109 



variegated, it is not Sa-mu-wa, it is not the wife of our Lord Tan-oo 

 Shan. Look at her accurately. If she be white and dresses in white, 

 she is the veritable Sa-mu-wa ; and he is the true Tan-oo Shan." 



Additions to the knowledge of Silk;— by Captain J. Mitchell 

 Superintendent of the Government Museum, Madras. 



[Received 9th October, 18G5.] 



In the year 1859, I had occasion to examine with the microscope 

 several kinds of raw silk, and I then discovered that the silk of A ntherea 

 paphia, commonly known as Tussah silk, had a very peculiar structure, 

 differing entirely from that of the several species of Bornbyx. 



My duties, up to a very recent date, left me no time for original 

 research and the Tussah silk was consequently put aside. It was not 

 however, forgotten, and I have taken advantage of the leisure afforded 

 by a holiday to endeavour to elucidate the structure of the filament. 



The silk of Bornbyx is cylindrical or nearly so. It is translucent 

 and, apparently, homogeneous. The larva spins a double filament ; 

 the two filaments, being laid side by side like two fine glass rods, are 

 held together by a gummy cement which is soluble in water. The 

 silk of Antherea papliia is flat, and appears to be composed of a number 

 of opaque rods placed side by side, the intervals between the rods 

 being filled in by a translucent cement, very difficult to dissolve.— 

 The filament is evidently compound. Under certain conditions of 

 illumination, it bears considerable resemblance to one of the coarser 

 bands of Hobert's Test Plate. 



This very peculiar appearance of the Tussah filament, is readily 

 seen with a quarter or half inch Achromatic ; but the demonstration 

 of its compound structure, in that exact way that will alone satisfy 

 the demands of science, is a more difficult matter, on account of the 

 insolubility of the cement which binds the elementary, or primary 

 filaments together. Macerating the silk in water for upwards of a 

 month did not separate them, alcohol did not do so. Acetic acid 

 mixed with alcohol appears to promise well ; but the only way in 



