OF THE ORDER ARANEIDEA. 253 
wound as it is generally supposed to be. Were I 
disposed to speculate upon the manner in which it 
affects insects on being introduced by the fangs into 
their vascular system, I might conjecture that it has 
a tendency to paralyze their organs of voluntary mo- 
tion, and to induce a determination of their fluids to 
the part injured; but I refrain from dwelling upon 
a suggestion, however plausible it may appear to be, 
which, in the present state of our knowledge of the 
subject, can only be regarded as hypothetical. 
4. Haperiments on Inanimate Substances. 
In the month of September 1846, litmus paper 
presented to spiders belonging to several genera when 
in a state of extreme irritation, having their fangs ex- 
tended, and the transparent fluid which issues from 
the fissure near their extremity conspicuously accu- 
mulated there, on being seized invariably became red 
as far as the fluid spread round the punctures made 
in it, a result clearly proving that this animal secre- 
tion, though tastless, is an acid. Care, however, must 
be taken, in conducting the experiment, not to suffer 
any fluid from the mouth to blend with: that which 
proceeds from the fangs, either before or after it has 
been transferred to the litmus paper, the former, ‘ren- 
dering the blue colour of the test more intense, and 
restoring it after it has been converted to red by the 
action of acetous acid, being decidedly an alkali; con- 
