Now to the Hymenoptera. I have not in my possession, I regret to say, any of those with whom my rearing-chambers used formerly to provide me, whether Honey-bee or Hunting Wasps. I have only a Green Saw-fly, whose larva lives in numerous families on the leaves of the alder. Reared under cover, this larva provides me with enough tiny black droppings to fill a thimble. That is sufficient: the urtication is quite definite. I take next the insects with incomplete transformations. My recent rearings have given me quite a collection of excretions emanating from the Orthoptera. I consult those of the Vine Ephippiger [24] and the Great Grey Locust. Both sting to a degree which once more makes me regret my lavish hand. We will be satisfied with this; indeed my arms demand as much, for, tattooed with red squares, they refuse to make room for fresh brandings. The examples are sufficiently varied to impose the following conclusion: the Processionary’s virus is found in a host of other insects, apparently even in the entire series. It is a urinary product inherent in the entomological organism. The dejections of insects, especially those evacuated at the end of the metamorphosis, contain or are even almost entirely composed of urates. Can the stinging material be the inevitable associate of uric acid? It should then form part of the excrement of the bird and the reptile, which in both cases is very rich in urates. Here again is a suspicion worthy of verification by experiment. For the moment it is impossible for me to question the reptile; it is easy, on the other hand, to interrogate the bird, whose reply will suffice. I accept what is offered by chance: an insectivorous bird, the Swallow, and a graminivorous bird, the Goldfinch. Well, their urinary dejections, when carefully separated from the digestive residua, have not the slightest stinging effect. The virus that causes itching is independent therefore of uric acid. It accompanies it in the insect class, without being its invariable concomitant every elsewhere. A last step remains for us to take, namely, to isolate the stinging element and to obtain it in quantities permitting of precise enquiries into its nature and properties. It seems to me that medical science might turn to account a material whose energy rivals that of cantharides, if it does not exceed it. The question appeals to me. I would gladly return to my beloved chemistry; but I should want reagents, apparatus, a laboratory, a whole costly arsenal of which I must not dream, afflicted as I am with a terrible ailment: impecuniosity, the searcher’s habitual lot. CHAPTER IX THE PSYCHES: THE LAYING In the springtime, old walls and dusty roads harbour a surprise for whoso has eyes to see. Tiny faggots, for no apparent reason, set themselves in motion and make their way along by sudden jerks. The inanimate comes to life, the immovable stirs. How does this come about? Look closer and the motive power will stand revealed.