THE MICROSCOPIC EXAMINATION OF BILK FIBRES. o7 



Preparation of the material for examination. — As has already been in- 

 timated, we were provided with no special apparatus for reeling the silk 

 from the cocoons, and specimens for the measurement of the fineness 

 and one set for determination of the tensile strength wefe obtained by 



simply cutting open the cocoons, separating the layers by pulling them 

 apart, and taking portions of fibre at random from each part, No at- 

 tempt was made to determine in this examination differences in the 

 quality of the fibre dependent upon the location of the part in the strati" 



tication of the cocoon, and hence the period of the spinning operation at 

 which it was formed, both because the time at our disposal for making 

 the examination had beeu limited and because this did not constitute 

 a principal object in the examination desired. There is no doubt, how- 

 ever, that an investigation with this regard would furnish results of 

 great interest and value. 



The fibres separated in this way were designated as t; dry : r that is, no 

 moisture was employed in their separation. Jt is well known that the 

 strength of the cocoon depends upon the glutinous character of the fibre 

 on the instant of its issue from the spinnerets of the insect, and that the 

 glutinous matter covering the fibre and forming a portion of its constit- 

 uent structure readily softens in warm water. And it is further well 

 known that this principle is applied practically in the industrial pro- 

 cesses of silk reeling. To determine what influence this may have upon 

 the fibre, we submitted a series of the cocoons to the action of warm 

 water, and when they were sufficiently softened secured the end of the 

 fibre and wound it upon slips of card-board, thus applying in a crude 

 way the process of reeling. The fibre so obtained has therefore been 

 designated as " wet."' The influence of the treatment to which the fibre 

 is subject in this process of separating it will be discussed later on, and 

 is manifest in the results given in Table II. 



Measurements of fineness. — If the fibre of raw silk be examined with a 

 microscope of sufficiently high power, it appears to consist of a more 

 or less flattened strip, somewhat depressed through the middle, so that 

 its cross-section may be likened to the longitudinal section of a dumb- 

 bell (co), as shown in the figure. This is explained by the fact that the 

 fibre in the glutinous condition is discharged by the worm in spinning, 

 from the spinnerets located on the under side of the head, near the man 

 dibles. As they pass out and are stretched by the worm m its to-and- 

 fro motions in spinning, the two fibres are cemented together more or 

 less firmly according to the rapidity of spinning. 



Sometimes these primary fibres, as they may be termed, are separate 

 and free from each other, and each is an almost perfect elongated cylin- 

 der. But in most cases they are firmly joined, and the two form a 

 compact whole, constituting the raw fibre of the cocoon. It is plain. 

 therefore, that this raw fibre is not cylindrical buf ribbon-shaped, and 

 that it has two lateral axes <>t' different lengths, so that on some accounts 

 a single measurement of a fibre does not represent its fineness, while .:: 



