We have seen that certain forms, for example, the poisonous spiders, not only secrete a toxine in their poison glands, but that such a substance may be extracted from other parts of their body, or even their eggs. There are many insects which likewise possess a poisonous blood plasma. Such forms have been well designated by Taschenberg as cryptotoxic (κρυπτος = hidden). We shall consider a few representative forms.
The Blister Beetles—Foremost among the cryptotoxic insects are the Meloidæ or "blister beetles," to which the well-known "Spanish fly" ([fig. 42a]), formerly very generally used in medical practice, belongs. The vescicating property is due to the presence in the blood plasma of a peculiar, volatile, crystalline substance known as cantharidin, which is especially abundant in the reproductive organs of the beetle. According to Kobert, the amount of this varies in different species from .4 or .5% to 2.57% of the dry weight of the beetle.
While blister beetles have been especially used for external application, they are also at times used internally as a stimulant and a diuretic. The powder or extract was formerly much in vogue as an aphrodisiac, and formed the essential constituent of various philters, or "love powders". It is now known that its effects on the reproductive organs appear primarily after the kidneys have been affected to such an extent as to endanger life, and that many cases of fatal poison have been due to its ignorant use.
There are many cases on record of poisoning and death due to internal use, and in some instances from merely external application. There are not rarely cases of poisoning of cattle from feeding on herbage bearing a large number of the beetles and authentic cases are known of human beings who have been poisoned by eating the flesh of such cattle. Kobert states that the beetles are not poisonous to birds but that the flesh of birds which have fed on them is poisonous to man, and that if the flesh of chickens or frogs which have fed on the cantharidin be fed to cats it causes in them the same symptoms as does the cantharidin.
Treatment of cases of cantharidin poison is a matter for a skilled physician. Until he can be obtained, emetics should be administered and these should be followed by white of egg in water. Oils should be avoided, as they hasten the absorption of the poison.
Other Cryptotoxic Insects—Though the blister beetles are the best known of the insects with poisonous blood plasma, various others have been reported and we shall refer to a few of the best authenticated.
One of the most famous is the Chrysomelid beetle, Diamphidia simplex, the body fluids of whose larvæ are used by certain South African bushmen as an arrow poison. Its action is due to the presence of a toxalbumin which exerts a hæmolytic action on the blood, and produces inflammation of the subcutaneous connective tissue and mucous membranes. Death results from general paralysis. Krause (1907) has surmised that the active principle may be a bacterial toxin arising from decomposition of the tissues of the larva, but he presents no support of this view and it is opposed by all the available evidence.
In China, a bug, Heuchis sanguinea, belonging to the family Cicadidæ, is used like the Meloidæ, to produce blistering, and often causes poisoning. It has been assumed that its vescicating properties are due to cantharidin, but the presence of this substance has not been demonstrated.