36 MR. J. BLACKWALL ON THE POISON OF 
These experiments do not present any facts which appear to sanction the opinion that 
insects are deprived of life with much greater celerity when pierced by the fangs of spiders 
than when lacerated mechanically to an equal extent by other means, regard being had in 
both cases to the vitality of the part injured, as the speed with which existence terminates 
mainly depends upon that circumstance. It is true that the catastrophe is greatly acce- 
lerated if spiders maintain a protracted hold of their victims, but this result is obviously 
attributable to the extraction of their fluids, which are transferred by oft-repeated acts of 
deglutition into the stomachs of their adversaries. 
From the entire mass of evidence supplied by the experiments taken in the aggregate, 
it may be fairly inferred that whatever properties characterize the fluid emitted from the 
orifice in the fangs of the Araneidea, it does not possess that degree of virulence which is 
commonly ascribed to it, neither is it so destructive to animal life when transmitted into 
a recent 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 paralyse their organs of voluntary 
motion, 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. Experiments 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 extended, and the trans- 
parent fluid which issues from the fissure near their extremity conspicuously accumulated 
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 secretion, though tasteless, 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, rendering 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; consequently, if both combined in due proportions, they 
would neutralize each other; but as there is usually a much more copious supply of the 
alkaline than of the acid fluid, its agency would predominate, and scarcely a trace of red 
would be discerned on the litmus paper. 
Submitted to the same chemical tests, the fluid contained in the stomachs of spiders 
and that Which flows from wounds inflicted on their bodies and limbs were found to be 
alkaline. Now if the frequency and suddenness with which large quantities of fluid are 
propelled into the mouths of spiders when occupied in extracting nutriment from their 
prey be borne in mind, the conclusion that they must be ejected from the stomach through 
the narrow @sophagus and pharynx seems to be inevitable *, as there is not any other 
