686 MR. P. R. AWATI ON THE MECHANISM 
MaTEeRIAL AND METHOD. 
I began my work in the Chelsea Physic Gardens of the 
Imperial College of Science, but, since the specimens were scarce, 
I had to go to Wisley, where I got good material through the 
kindness of Mr. F. Chittenden, the Director of the Wisley 
Horticultural Laboratory. 
The following reagents were used for fixing the insects :— 
(i.) Bouin’s solution, 
(ii.) Carnoy solution (Formula No. IJ), 
(iii.) Petrunkevitch solution ; 
and all of these have given satisfactory results. 
The insects were kept in the fixing reagent for 24 hours, and, 
without being passed through the lower grades of alcohol, were 
thrown into 90 per cent. alcohol, in which they were allowed to 
remain for several weeks. Thus treated, they were sufficiently 
hardened for section-cutting, and it was, therefore, not necessary 
to keep them in absolute alcohol for more than three hours. After 
immersion for. one hour in a mixture of equal parts of absolute 
alcohol and chloroform, they were transferred to pure chloroform, 
in which they were left for 24 to 36 hours. They were now 
imbedded in paraftin-wax (melting-point 56° C.) in the following 
way :—A saturated chloroform solution (in the cold) of wax of 
the same melting-point was prepared and the specimens were 
allowed to lie in it for two or three days at the temperature of 
the laboratory. They were then transferred to pure molten wax 
in the oven, where they remained for five hours. A block was 
then prepared in the usual way. 
The importance of attention to the details of the above routine 
cannot be overrated. There is in the literature, so far as I can 
find, no single detailed description of a method by which good 
sections of hard insects can be got, and it is notoriously difficult 
to find any but diagrammatic illustrations to the papers of those 
who have investigated such forms. As the result, however, of 
my experiments, | have found that it is possible to obtain series 
of excellent sections, not only of Zygus, but of such hard and 
thickly-chitinised insects as the bed-bug, without using any 
reagent for softening the chitin. I am therefore justified in 
giving some prominence to the technique. 
Long soaking in a mixture of chloroform and wax was found 
to be the only way to obtain proper impregnation, and the time 
given is the optimum—a shorter time is insufficient, a longer 
causes the tissues to become brittle. The length of the soaking 
differs with different imsects, according to the quality of their 
chitin. 
The sections were stained, in the ordinary way, with Ehrlich 
hematoxylin, orange G, and picric acid (saturated solution in 
90 per cent. alcohol). 
For macerating purposes, potash (10 per cent.) was used. A 
few drops of acetic acid were found useful. The specimens were 
