The confirmatory arguments are so urgent that we are at first tempted to answer:
“Yes, the adult will resist.”
But we will leave experiment to speak for itself. With this object preparations are made with four sets of subjects. The first consists of twelve Cetonia-larvæ, which, after being stung in October, have been revaccinated, that is to say, stung a second time, in May. The second set is also composed [[107]]of twelve Cetonia-larvæ, but these have been stung once only, in May. Four chrysalids of the Spurge Hawk-moth form the third. They belong to caterpillars stung once, in June. Lastly, I have some cocoons spun by the Silkworm whose vaccination, attended by a flow of blood, I have described above. The Scorpion will once more play his part with each lot after the hatching has taken place.
The Silkworm Moth is the first to respond to my impatience. The Moth is there in two or three weeks’ time, bustling about in readiness for the pairing. The stab received as a caterpillar has not cooled his ardour in the very least. I subject him to the test. The attack is laboured and the blow is not clearly struck. No matter: all those attacked perish after a death-struggle lasting a day or two. The previous vaccination has made no difference to the result: they succumbed before and they succumb after.
But these are feeble witnesses, on whom it is not wise to rely. I shall achieve more, I feel convinced, with the Hawk-moths and especially with those sturdy subjects the Cetoniæ. [[108]]Well, the Hawk-moths whose caterpillars have received the virus which theoretically should render them immune retain their normal vulnerability: when attacked by the sting, they succumb instantly, exactly like the others, who did not at the larval age undergo a preventative inoculation.
Perhaps the number of days elapsing between the stinging of the caterpillar and of the moth was not sufficient to enable the virus to act upon the organism to the requisite degree. It might need a longer space of time to bring about the inward modifications caused by the action of the poison on the insect’s organism. The Cetonia-larvæ will perhaps be able to dispense with this period.
I have a set of twelve of them, stung twice over, first in October and then in May. The perfect insect bursts its cocoon at the end of July. Ten months therefore have elapsed since the first sting and three months since the second. Is the adult now immune?
Not at all. When subjected to the Scorpion, my twelve vaccinated specimens all perish, no more and no less quickly than their fellows who were born quietly in their heap of rotten leaves. Twelve others, pricked [[109]]only once, in May, succumb with the same promptness. In the case of both sets, my devices, which inspired me with confidence at first, miscarry pitifully, to my extreme confusion.
I try another method, that of transfusion of blood, which is related to serotherapy. Since it resists the Scorpion’s sting, the larva of the Cetonia must have blood endowed with special qualities, apt to neutralize the virulence of the poison. If transferred from the larva to the adult, might not this blood communicate its qualities and render the perfect insect invulnerable?
I give a Cetonia-grub a superficial wound with the point of a needle. The blood spouts forth abundantly. I collect it in a watch-glass. A glass tube of small diameter, drawn out to a sharp point, serves as an injector. I charge it by suction with the fluid collected, varying the dose from a cubic millimetre to ten and twenty times as much. By blowing into the tube I transfer the liquid into some point of the adult Cetonia, particularly on the ventral surface, where a needle has prepared the way for the fragile injector. The insect stands the operation [[110]]very well. The richer by a little larval blood and not seriously wounded, it presents every appearance of blooming health.