March 1, 1873 ] 
THE FHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
681 
THE COLOUR OE THE WING CASES OE 
CANTH ARISES. 
BY HENRY POCKLINGTOX. 
As every one knows wlio has read the B. P. de¬ 
scription, Cantharis vesicatoria is furnished “ with 
two wing-covers of a shining metallic green colour.” 
This characteristic holds good only when dried 
insects are looked at in a certain way, for it happens, 
as perhaps many readers know, that by properly 
managing matters it is possible to see these wing- 
cases of almost any colour. For instance, if one be 
examined by lamplight, the colour varies very sen¬ 
sibly as the positions of the lamp or wing-case are 
varied with respect to each other. These variations 
are much intensified when a wing-case is immersed 
in alcohol or carbon bisulphide in a narrow test- 
tube, and the test-tube containing the case held so 
that the lamp is between, but in a line or nearly so, 
with the eye, the colour appears no longer green but 
a rich golden copper. Slightly varying the position 
of the tube, the colour changes to a more decided 
yellow, and quickly to green. Again changing the 
position, the colour appears to be a beautiful blue, 
and then a purple. A peculiarity of shade in these 
last colours induced me to test the light with a 
Nicol prism. In two positions of the prism the 
light was nearly wholly quenched. In two other 
positions it was transmitted. I quench the light and 
lower the slide, the green appears; I slightly turn 
the Nicol, the green is partially quenched and be¬ 
comes more yellow. I interpose the Nicol between 
the light and the wing-case, and I find that in two 
positions of the prism I cannot obtain the blue 
colour, and that these positions of the prism are 
complementary to those in which the blue light was 
previously quenched. Whence it is quite clear that 
whatever causes the blue colour, it is something 
which alters the plane of vibration of the reflected 
light. So far for lamplight. 
If I view the wing-case by daylight, I find the 
blue is much more intense, and using the magne¬ 
sium light, that it is even more beautiful; whence 
it may be suspected that this blue colour is due 
either to fluorescence, or to dispersion by reflection. 
I think it is probably due to both. The purple and 
the major part of the blue are clearly due to reflec¬ 
tion, otherwise the interposition of a Nicol between 
the light and the wing-case would not so nearly 
quench it as it does. That the Nicol so placed does 
not wholly quench the light goes a long way to show 
that part of the colour is due to reflection ; and the 
fact that when the emergent blue light is examined 
by a Nicol, it is never wholly quenched, nor wholly 
transmitted, I think places the matter almost in the 
region of certainty. The blue is not a pure blue; 
it contains a little green; and this is pretty constant 
however the wing-case may be viewed by reflected 
light. . So we may suspect that although most 
of the colours of the case, as variously viewed, are 
due to interference, or selective dispersion by re¬ 
flection, or to lowering of refrangibility if fluores¬ 
cence be also a factor, there is also what we gene¬ 
rally denominate a colouring matter—a substance 
that is persistently selective and sends out, in this 
case, light with a continued balance on the green 
side of the account. With a view to ascertaining 
the natiu’e of this colouring matter, a few wing- 
cases were immersed in ether, in alcohol and in 
TniRD Series, No. 110. 
water for several days, and these fluids were ex¬ 
amined spectroscopically. 
Ethereal Solution .—A small quantity placed in a 
specimen tube, or homoeopathic pilule tube, and ex¬ 
amined by a Sorby Browning spectroseope, or a stu¬ 
dent’s stand spectroscope, kindly lent me by Mr. J. 
E.Winspear for the purpose. (A micro-spectroscope is 
the more convenient instrument for use in these re¬ 
searches, but it is advantageous to check the reading 
of one instrument by another.) I was much surprised 
to see a sharply defined band in the red, suggestive 
at once of a chlorophyll band I once saw, but un¬ 
happily could never trace the origin of, and a shaded 
band in the green with partial absorption of the 
blue, and general absorption beyond. In other 
words, there was a well-defined narrow absorption 
baud at 11- of Sorby’s scale, a shaded band extending 
each side of 5J, and the partial and general absorp¬ 
tion already spoken of. In many respects the spec¬ 
trum resembles that of the privet, and exactly cor¬ 
responds with that given by the chlorophyll of a 
portion of a leaf I examined some time since, but 
have not as yet succeeded in tracing. It differs 
from the privet spectrum as given to Herapath’s dia¬ 
gram in the presence of the shaded band at 5£, and 
also, if the diagram be correctly printed, very slightly 
also in the position of the band at 1^. 
Alcoholic Tincture .—The spectrum of this is 
essentially similar, excepting that the shaded band 
at 51 is absent. 
The Aqueous Solution gives an entirely different 
spectrum. There is general absorption of the 
violet head of the spectrum and no well-defined 
bands (entire absorption from '& to violet; shaded 
or partial absorption, 8 to 7). The wing-cases re¬ 
moved from the water, dried and digested in alcohol, 
give a well-defined band at 1|-, and general and par¬ 
tial absorption as in the alcoholic tincture, the 31 
sliaded band being absent. Ether added after alco¬ 
hol has been removed gives the shaded band by 
daylight, if care be paid to adjust the slit very 
exactly, and to focus sharply for that part of the 
spectrum. 
There are thus, I think,’ grounds for concluding 
that the green colouring matter (the green oil of 
some analyses) is due to chlorophyll, and it is an 
interesting question whether the spectrum (the II, 
51 shaded and absorption beyond 8) characteristic 
of this will not be found to vary in ethereal tinc¬ 
tures prepared from cantliarides collected from off 
different feeding grounds. And it is with a view of 
suggesting the inquiry to those who, perhaps, have 
more leisure and better opportunities of procuring 
the raw material than I have, that I send the fore¬ 
going rough and incomplete notes for publication. 
The reagents that I have used, c.y., sulphide of 
soda, ammonia, acids and iron salts, do not give re¬ 
sults which permit at present of reduction into 
conformity with each other, and I reserve any ac¬ 
count of them for a future paper which will include 
an account of the colouring matter of the contents 
of the stomach, of the thorax and other parts not 
now noticed; I will only remark that so far 
they confirm my opinion as to the clilorophyll na¬ 
ture of the green colouring matter. 
In conclusion, I may just remind my readers that 
the reference spectrum spoken of is that devised by 
Mr. Sorby, and described by him in Dr. Beale’s 
‘How to Work with the Microscope,’ 4tli ed., page 
225, and is an interference spectrum produced by 
