[CHAPTER XXXIV]
Return to St. Léger-en-Yvelines — Norka — Studies on the death of the silk-worm moth — War declared — Mobilisation.
The drawback of the holidays consisted, for Metchnikoff, in coming away from his laboratory and in the impossibility of following his diet in a hotel or a boarding-house. We therefore resolved to hire a cottage in some quiet place, to organise a small laboratory, and to continue our usual mode of life.
St. Legér-en-Yvelines, where we had spent part of the preceding summer, answered all our requirements. We took a small villa there and called it “Norka,” which means in Russian “little hole,” “little refuge,” and came there for the holidays in July 1914.
Elie seemed pleased to be there; thanks to the laboratory, he could easily vary his occupations, for continuous reading fatigued him. His reflections having led him to the problem of natural death, he had for some time been seeking for a subject on which he could study the mechanism of the phenomenon. He had formerly studied the May-flies (Ephemeridæ), predestined to a natural death by their rudimentary buccal organs, incapable of use in feeding. But the life of those insects, a life of a few hours or a few days at the most, was too short to allow the necessary researches. The males of the Rotifera, which are also deprived of buccal organs and even of digestive organs, were too small in size for physiological experiments. Thus, those two examples of natural death among multicellular beings were unsuitable to the projected study.
He found a more favourable subject in the moth of the silk-worm (Bombyx mori); the rudimentary buccal organs of that insect make all feeding impossible and predestine it to a natural death. The dimensions of the silk-worm moth are large enough and it has a life duration of twenty-five or thirty days, therefore sufficient to allow the study of the mechanism by which its death is brought about. Metchnikoff procured a quantity of silk-worms, and soon the moths hatched and covered all the mantelpieces and tables in Norka with white flakes. He ascertained that it was not hunger which brought about the death of the moths, for their organism was not in the least exhausted.
The nutrition of the latter takes place at the expense of the fatty substance which remains after the metamorphosis of the chrysalis into a moth. The dissolution of this fatty substance produces toxins which pass into the urine. Thus the obvious cause of the death of the moth is an acid intoxication by toxic urine secreted in the bladder. As the latter does not empty itself, uræmia becomes inevitable.
The majority of moths contain no micro-organisms which could suggest death by infection.
The only theoretic objection against a natural death might consist in the existence of “invisible microbes.” Indeed, the question of invisible microbes revealed in certain infections perturbed Metchnikoff’s mind to such an extent that, during his last illness, he used to say that it would have been a curse to his ulterior activity, a sort of ghost preventing all definite conclusions in problems connected with the absence or presence of microbes. The last word on natural death, he said, will only be spoken when, owing to the improvement of the microscope, those microbes which are as yet invisible to us will become visible. Nevertheless, as far as can be judged at present, the death of the Bombyx mori is due, not to external causes, but to the structure of the insect itself, and is therefore a natural death.