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. [[161]]
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. [[162]]
And, first of all, does the Pine Processionary possess a special glandular structure which elaborates the virus, as do, for instance, the poison-glands of the Wasps and Bees? By no means. Anatomy shows that the internal structure of the stinging caterpillar is similar to that of the harmless one. There is nothing more and nothing less.
The poisonous product, of unlocalized origin, results, therefore, from a general process in which the entire organism is brought into play. It should, in consequence, be found in the blood, after the manner of urea in higher animals. This is a suggestion of grave import, but after all quite valueless without the conclusive verdict of actual experiment.
Five or six Processionaries, pricked with the point of a needle, furnish me with a few drops of blood. I allow these to soak into a small square of blotting-paper, which I then apply to my fore-arm with a waterproof bandage. It is not without a certain anxiety that I await the outcome of the experiment. The result will show whether the conclusions already forming in my mind will receive a solid basis or vanish into thin air.
At a late hour of the night, the pain wakes [[163]]me, a pain which this time is an intellectual joy. My anticipations were correct. The blood does indeed contain the venomous substance. It causes itching, swelling, a burning sensation, an exudation of serum and, lastly, a shedding of the skin. I learn more than I had hoped to learn. The test is more valuable than that of mere contact with the caterpillar could have been. Instead of treating myself with the small quantity of poison with which the hairs are smeared, I have gone to the source of the irritant substance and I thereby gain an increase of discomfort.