What the direct contact of the caterpillar did not teach me the artifices of chemistry will demonstrate with a violence which I was far from expecting. I treat the caterpillar with ether, just as I treated the slough of the Pine Processionary. The number of the creatures taken for the infusion—they are pretty small as yet, are scarcely half the size which they will attain when mature—is about a hundred. After a couple of days’ maceration, I filter the liquid and leave it to evaporate freely. With the few drops that remain I soak a square of blotting-paper folded in four and apply it to the inner surface of my fore-arm, with a thin rubber sheet and a bandage. It is an exact repetition of what I did with the Pine Processionary. Applied in the morning, the blister hardly takes effect until the following night. Then by degrees the irritation becomes unendurable; and the burning sensation is so acute that I am tormented every moment with the desire to tear off the bandage. However, I hold out, but at the cost of a sleepless, feverish night. How well I now understand what the woodcutters tell me! I had less than a square inch of skin subjected to the torture. What would it be if I had my back, shoulders, neck, face and arms tormented in this fashion? I pity you with all my heart, you labourers who are troubled by the hateful creature. On the morrow, the infernal paper is removed. The skin is red and swollen, covered with tiny pimples whence ooze drops of serous fluid. For five days the itching persists, with a sharp, burning pain, and the running from the pimples continues. Then the dead skin dries and comes off in scabs. All is over, save the redness, which is still perceptible a month later. The demonstration is accomplished; the Arbutus Caterpillar, capable as he is of producing, under certain conditions, the same effects which I obtain by artificial means, fully deserves his odious reputation. CHAPTER VIII AN INSECT VIRUS One step forward has been taken, but only a very little one as yet, in the problem of the stinging caterpillars. The drenching with ether teaches us that hairiness plays a very secondary part in the matter. With its dust of broken bristles, which the least breath wafts in all directions, it bothers us by depositing and fixing its irritant coating upon us; but this virus does not originate in the creature’s fleece; it comes from elsewhere. What is the source of it? I will enter into a few details. Perhaps, in so doing, I shall be of service to the novice. The subject, which is very simple and sharply defined, will show us how one question gives rise to another; how experimental tests confirm or upset hypotheses, which are, as it were, a temporary scaffolding; and, lastly, how logic, that severe examiner, leads us by degrees to generalities which are far more important than anything that we were led to anticipate at the outset.