488 
LEPIDOPTUliA. 
is not attacked by either pepsin or trypsin, while by strong acids or 
alkalies it is converted into albumoses or albuminates. The silk coverings 
of wasp cells and spider’s webs give the reactions and show the solubili¬ 
ties of fibroin (Engel and Schlossberger). 
Sericin resembles ordinary gelatin in its solubility, but does not 
gelatinise so readily and is precipitated by acids. The presence of 
glycocoll is doubtful, while tyrosin and serin are abundant. 
PERCENTAGE COMPOSITION. 
Glycocoll (Amino-Acetic acid). 
Alanin (Amino-propionic acid). 
Leucin (isobutyl-«-amino-acetic acid). 
Phenylalanin. 
Prolin (a-Pyrrolidin-carboxylic acid). 
Glutaminic acid, («-Amino-normal 
glutaric acid). 
Aspartic acid (Amino-succinic acid). 
Serin («- Amino-/l-hydroxy-propionic 
Gelatine. 
Sericin. 
Fibroin. 
16*5 
0T-0-2 
36*0 
0"8 
5-0 
21*0 
2-1 
present 
1-5 
0-4 
1*5 
5*2 
0-3 
14*0 
0*56 
acid). 
present 
6*6 
1-6 
Hydroxy-pyrrolidin carboxylic acid 
(<;, ii, no,). 
Lysin(e diamino-normal-caproic acid). 
3-0 
5*5 
present. 
present. 
Histidin. (C 6 H 0 N s O .) 
•4 
present. 
Arginin (Guanidin-«-amino-valerianic 
acid). 
9*3 
4-0 
1*0 
Ammonia. 
•43 
1-87 
Tyrosin (phenyl-«-hydroxy-a-amino 
propionic-acid). 
5-0 
10-0 
The weight of silk produced. —In the cocoon the relative weight of 
silk formed is shown from the following figures of three Eri cocoons 
(Attacus ricini). 
Full-grown larva. 
126. grains. 
91-6 
101. 
Cocoon, etc., at emergence. 
47-4 
36-8 
38*8. 
,, ,, after ,, 
8-2 
6*8 
6*0. 
Pupa case, etc. 
1-1 
•8 
•9. 
Cocoon. 
7'1 
5-8 
4*9. 
It has been found that in Eri silk 75 to 90 pounds of leaf must be fed 
to worms to produce a pound of silk. 
The following are the more important characteristics of the four 
commercial Indian silks :— 
