DoBSON_, on Laap, or Lerp, 
129 
crenate ridges (fig. 9 b), wMch present a beautiful appearance 
under the microscope. The hair is apparently solid and 
homogeneous throughout^ and certainly not tubular as stated 
by Dr. Anderson. 
2. With respect to the chemical composition of the crusty 
it would appear^ from the action of reagents^ to present all the 
properties of pure starch. It is turned blue by iodine, is 
unacted upon by cold water, and with difficulty dissolved in 
boiling water, and then not wholly, a sort of membranous 
residue being left as in starch grains. Alcohol and ether in 
the cold have no effect upon it. The sweetish taste percep- 
tible when a portion of lerp is placed upon the tongue may 
probably be due to the rapid conversion of the amyloid sub- 
stance into sugar, under the influence of the saliva. 
In the Paper by Dr. Anderson, above referred to, a more 
complex composition is assigned to this substance. But it is 
not improbable that the samples of lerp operated on by that 
chemist might have undergone some change, and thus have 
contained more highly oxidized compounds than appear to exist 
in the unaltered crusts. One thing is perfectly certain, that 
the entire substance is coloured blue throughout, and homoge- 
neously, by a watery solution of iodine, and that in cold water 
no change whatever is effected in it. Dr. Anderson^s state- 
ment, moreover, that starch grains, in the usual sense of that 
term, are contained in lerp, does not accord with our obser- 
vations either upon the white or yellow kinds. The substance, 
in short, appears to be constituted of a homogeneous amyloid 
substance which, from its morphological characters, would 
seem to be spun out of the body of the larva in a semifluid or 
glutinous condition, and afterwards to harden into the trans- 
parent vitreous substance of which the crusts are composed. 
Dr. Anderson states that the lerp (white) examined by him 
consisted of — 
Water . 
. 15-01 
Sugar (grape) 
. 49-06 
Gum 
. 5-77 
Starch . 
. 4-29 
Inulin . 
. 13-80 
Cellulose 
. 1204 
100 00 
The fact that many species of Psylla and other homopterous 
insects afford starchy and sugary secretions is notorious, 
though no very precise chemical examination of most of 
these substances appears hitherto to have been made. A 
familiar instance of the kind is presented in the Honey -dew 
