Elie still had his Licentiate thesis to prepare. In order to do so, he decided to spend two months in the island of Heligoland, of which the flora and fauna were very attractive to naturalists. In spite of his previous failure, his parents made no objection to his departure; they gave him the little money they could spare and Elie started, in 1864.

As soon as he arrived in Heligoland he became absorbed in his work. He proceeded with his idea of bringing light upon the genealogy of organisms through the study of isolated forms outside definite groups.[7]

His ardour in his work attracted the attention of several German scientists, one of whom introduced him to the celebrated botanist Cohn, who soon became interested in him. During the walks which they took together, they held scientific conversations full of interest for the youth. Cohn advised him to work under the celebrated zoologist Leuckart. Elie received this counsel with enthusiasm, but there was a great difficulty, which was the lack of money to prolong his stay abroad. He did not wish to ask for more from his parents and decided on the following plan, which he expounded in the following letter to his mother, the constant confidante of all his aspirations:

He did not tell his mother that he never had enough to eat. Neither did he wish Cohn and his other acquaintances at Heligoland to notice it, and he carefully concealed his style of living.

He went to Giessen for the opening of the Naturalists’ Congress and read with success two papers dealing with his researches at Heligoland. Engelmann (who was to become well known as a physiologist) and he were the youngest members of the Congress, and their extreme youth attracted general attention. Elie at last made Leuckart’s acquaintance; he was charmed by him and definitely decided to begin at once to work under his direction, and, as his stay abroad had thus to be prolonged, he asked and obtained a bursa from the Russian Ministry of Public Education.

The results of his researches at Heligoland had led him to suppose that the Nematodes (of the worm type) formed an independent group; he now proposed to settle that question. Leuckart allowed him to work in his laboratory during his absence for the holidays; Elie immediately set to work and discovered a very curious and quite novel case of alternation of generations; hermaphrodite and parasitic Nematodes giving birth to a free bisexual generation.

Delighted with his discovery, he hastened to communicate it to Leuckart, who was incredulous at first but had to give way to evidence when Elie showed him all the intermediary stages. Still the German scientist was obviously annoyed that this discovery should have been made in his absence and independently from him. He proposed to the young man that they should continue researches in collaboration and publish a joint memoir. Elie accepted joyfully. In his ardour he worked too much, and fatigued his eyesight so that he was forced to limit his microscopical researches to a few hours a day, and Leuckart advised him to take a rest.

It happened that Elie’s brother Leo had just settled in Geneva and invited him to stay with him; Elie started to join him. The brothers had not met for a long time. Leo had been travelling and had resided in many different places. He was an extraordinarily gifted man, impulsive, brilliant, and artistic, but restless and incapable of adhering to a steady course of action; he scattered his activities and did not therefore produce all that his rich nature was capable of. He had a remarkable gift for languages; he knew not only a number of European languages but also several Oriental languages, having been in the East, where he had occupied a post of agent in navigation and commerce. He afterwards lived in Italy, took an active part in the Garibaldi movement and was wounded. A clever painter, he also had real literary talent; handsome, witty, agreeable, he was a most attractive personality. Elie had great affection for him.

He found him surrounded with young men and studying a map. They were discussing the acquisition of a piece of ground in Italy in order to found a socialistic community, and Leo, who knew the country, was to choose the locality. Elie was at once made acquainted with the political questions of the day; the young scientist was unfavourably impressed, for the whole reduced itself to party questions and dogmatic discussions founded on hollow grounds. Accustomed as he already was to positive scientific methods, vague and arbitrary theories could not satisfy him.

On the other hand, he was deeply impressed by the personality of the celebrated socialistic Russian writer, Herzen, who resided in Geneva at that time. The young revolutionaries considered him as too literary and too much of a theoretician; they themselves yearned for a direct-action policy. Leo Metchnikoff, however, admired him fervently. Meetings often took place in Herzen’s rooms; he used to read to his guests with wonderful effect his yet unpublished manuscript PassÉ et pensÉes. A great and powerful figure, the superiority of his intelligence was almost crushing, while his sparkling wit and the nobility of his whole being endowed him with an incomparable and irresistible personal charm. Metchnikoff often said that no man had left a deeper impression on his life. As a politician, however, he had not the same prestige in his sight.

This sojourn in a revolutionary centre interested him much, but had the result of confirming his conviction that science was immeasurably superior to politics, and he congratulated himself on the path he had chosen. After he had rested, he started to return to Giessen and stopped at Heidelberg, a centre for Russian students who gathered around Helmholtz, Virchow, and Bunsen. He hurried to the library in order to see scientific periodicals; one of the first that came under his eyes was a number of the GÖttingen News, containing a memoir by Leuckart on the Nematodes which they had studied together; Leuckart described, in his own name, their common researches and also those personal to the young man, whom he only mentioned incidentally. Elie was shocked and indignant. On his return to Giessen he tried to obtain an explanation from Leuckart but in vain; the latter eluded his questions and gave him no answer.[8]

In his despair, the youth confided in Claus, a professor of zoology whose acquaintance he had made at the Congress, who told him that Leuckart was in the habit of such dealings, and urged Elie, as an independent stranger, to reveal the fact. He pressed this with so much insistence that Elie ended in following his advice; he sent an article stating the case to Dubois-Reymond’s journal. He then departed from Giessen without taking leave of Leuckart.

Having had a bursa of 1600 roubles a year granted him for two years by the Russian Ministry of Public Instruction, he was able to undertake a journey to the shores of the Mediterranean in order to pursue his researches.

He had heard of a very talented young zoologist, Alexander Kovalevsky, who also knew him by hearsay and had written him a letter full of enthusiasm concerning the rich Mediterranean fauna and the facilities for work in Italy. He therefore went to Naples on leaving Giessen. Though the journey in itself had but a secondary attraction for him, he had expected to receive a strong impression; but his imagination had painted such grandiose pictures of the country that he had to cross, that the reality disappointed him, and Italy, like Switzerland on a former occasion, fell very far short of his expectations. He stopped at Florence, which made but a poor impression on him. Museums fatigued him, for he saw a great deal too many works of art all at once without any previous preparation. Architecture and the plastic arts in general did not take any hold of him. During his rapid journey he only saw the country quite superficially and had no time to become impregnated with its beauty. He therefore hastened towards Naples, where his work and Kovalevsky attracted him far more.

He found in Kovalevsky a young man with shy but cordial manners and the clear sweet eyes of a pure child, obviously an idealist. He had for science an absolute cult, the sacred fire of the worshipper; no sacrifice was too great, no difficulty too repellent for his ardour. On a closer acquaintance, the small, timid young man proved to be a hard fighter where science was concerned. The two young men formed an excellent impression of each other, and a friendship was started between them which was to last a lifetime. Though very different from each other, they met on common ground, a passion for science. They worked with the greatest energy, going together on zoological excursions, exchanging their ideas, discussing their aspirations; a similarity of tastes lent great attraction to their friendship.

At Giessen, Elie had read Fritz MÜller’s For Darwin, a book which had a decisive influence on the future direction of his researches. Fritz MÜller, in his embryological works on certain crustaceans, had been the first to confirm in a concrete manner Darwin’s evolutionist theories; he had thus demonstrated that it was chiefly in embryology that precious indications were to be found concerning the genealogy of organisms.[9] Under the influence of this work, Elie, who until now had limited himself to introductory researches, resolved to concentrate all his efforts on the comparative embryology of animals. He started to work in that direction, and his researches confirmed him more and more in the opinion that the key of animal evolution and genealogy was to be sought for in the most primitive stages, in those simple phases of development where no secondary element has yet been introduced from external conditions. In those primordial stages, essential characters, common to all, reveal the analogy and connections between animals from different groups.

Every animal begins by being unicellular, for the egg-cell, the reproducing cell, common to all, corresponds to a unicellular being. It is only after fecundation, when it has become an ovum, that this first cell evolves by dividing itself into consecutive segments, each of which is a new cell. This phenomenon is analogous with the multiplication of unicellular beings through division; only, those segments of the ovum do not separate but constitute a whole under the aspect of a hollow sphere, called a blastula, which is the first manifestation of a multicellular being. This blastula is formed of superposed layers, each of which gives birth to specialised organs in the embryo. The outside layer, or ectoderm, produces teguments and the nervous system; the internal layer, or endoderm, gives birth to endothelial cells, the digestive and internal organs; between those two layers comes a third, intermediary layer, the mesoderm, from which the skeleton is developed and also the muscle and blood tissues.

The evolution of these layers in Vertebrates was well known, but very little so in Invertebrates, though it is only through the development of inferior forms that the origin and general evolution of living beings can be elucidated. That is why, during many years, the principal theme of Metchnikoff’s researches was the comparative study of the embryonic layers of inferior animals and the ulterior fate of their constituting elements. By following this train of thought, he was able to demonstrate that the development of lower animals takes place on the same plan and follows the same laws as that of higher animals; thus, that there is a real communion between all living beings, which is the concrete confirmation of the theory of evolution.

By their work, Kovalevsky and Metchnikoff contributed to the foundation of Comparative Embryology. The comparative study of cells produced from the divers embryonic layers, and observations on the ulterior development of the functions of those cells, gradually led Metchnikoff to his theory of phagocytes and to pathological biology. An uninterrupted thread can be followed right through his life-work, from the beginning until the end.

In spite of his absorbing work he took great interest in his surroundings, and during this first stay in Italy he became acquainted with two interesting personalities, Bakounine the anarchist and the celebrated physiologist SetchÉnoff. Both resided at Sorrento. Kovalevsky and Metchnikoff, who greatly desired to know them, decided to call on them, after much hesitation.

Bakounine, a giant with a leonine head and a thick mane of grey hair, struck them as being a fiery enthusiast but an intolerant sectarian, easily roused; for instance, any small and unimportant local meeting was enough for him to predict an imminent revolution in Russia. His theories were epitomised in these words, “We must not leave stone upon stone”; but when asked what should be built up on those ruins he could only say, “We shall see later.” Elie looked upon him as a force powerful by its fire and vitality, but thought his mind neither judicial nor profound.

Very different was the impression produced on him by SetchÉnoff. He carried great weight through the depth of his intelligence, his persuasive eloquence and general thoroughness. He was of a Mongol type and his features were plain, but his splendid eyes, deep and intelligent, shrewd and yet kindly, illumined his face with an unforgettable inward beauty. When Elie went to see him, it was with the uneasy feeling that his own knowledge of chemistry and physics was very restricted, having been very superficially acquired during his rapid passage through the University. In spite of this cause for bashfulness, a mental compact and exchange of ideas was immediately established between the two, and a sympathy was born between them which developed into a lifelong friendship. Elie expatiated upon his plans for the study of the embryology of inferior animals from the evolution point of view, and received from the older scientist much encouragement, for which he never ceased to be grateful.

He worked a great deal during this first stay at Naples, in spite of periods of great fatigue. As a relaxation, he plunged into philosophical reading. After Kovalevsky’s departure, he joined Bakounine’s circle, the members of which took their meals in a restaurant which rejoiced in the sonorous name of Trattoria della Harmonia. In the autumn of the year 1865, a cholera epidemic broke out in Naples. Every one was nervous and depressed, and this general depression was increased still more by some of the customs of the country—continuous lugubrious church bells, funeral processions in which penitents took part, carrying smoking torches and wearing hoods over their heads with holes for their eyes, etc. Elie, on whom the epidemic had made a great impression, was even more disturbed by the death of one of the members of their little circle, a popular Englishwoman, liked by everybody. She had no fear of cholera and was bright and merry. But one day she did not come to the Trattoria della Harmonia; she had been struck by the scourge and was dead the next day.

Elie was so struck by her death that his nerves, already very tense, gave way and he left Naples, being, moreover, worn out with overwork.

He started for GÖttingen, for he wanted to begin the study of Vertebrates under the direction of Professor Keferstein. Keferstein straightway gave him a valuable lizard specimen to anatomise. Elie was not good at technique, on account of his nervous temperament; he used occasionally to lose his patience and his temper, to that point that he flung his material across the room. It happened so on this occasion; having completely wasted the valuable lizard, he conceived a still greater horror of technique and soon left Professor Keferstein for Henle, the celebrated anatomist. He worked with him for a short time at the histology of frogs’ kidneys, a subject chosen by the Professor. Soon the young man realised that he was no longer capable of submitting to school discipline and resumed his independent researches. When he had to do with those problems which absorbed him he was always able to conquer his aversion for technique and to do what was required. He studied the embryology of the green-fly from the genealogical point of view, and went to Munich for the summer term in order to work with the celebrated zoologist von Siebold, a typical and venerable old German scientist. The latter was too old already to be troubled with pupils, and Elie studied his insect embryology independently; however, he visited the old man assiduously, and they had long scientific conversations. Their relations were always extremely cordial, and they even kept up a regular correspondence for many years.

During his stay in Germany, music was the young man’s only recreation. He did not play any instrument; his parents, discouraged by the failure of their elder children, had not had him taught, and besides, his precocious vocation would have left him no time. Yet he certainly had a natural talent for music, which he passionately loved. He could only whistle, but with that feeble means succeeded in reproducing complicated compositions. Having assiduously attended excellent concerts, he had made himself thoroughly acquainted with classical music, and Beethoven and Mozart always remained his favourite composers. His stay in Germany taught him to appreciate the great capacity for work of the scientists of that country; he admired the organisation of their laboratories, allowing every force, great or small, to be utilised and making useful collective work possible in those complicated researches which demand the collaboration of divers specialists. On the other hand, he felt a great aversion for the manners and customs of German students. Their corporations, duels, and long sittings in beer-houses were distasteful to him; he could not understand how these coarse “Burschen” could become transformed into cultivated intellectuals and respectable scientists. People to whom he expressed this wonder merely said, “Youth must have its fling....” Moreover, scientists themselves were not particularly courteous to each other. More than anywhere else personal questions held a foremost place, and kindliness was rare between colleagues.

After staying some time in Munich, Elie returned to Naples, war having broken out between Northern and Southern Germany. This time, in order to spend less on the journey, he took a steamer at Genoa, but with fatal results, for a storm was raging; he suffered a great deal, and, when he reached Naples, violent fits of giddiness made him incapable of doing any work at all for some time. Cholera reappeared, and the landlady of the rooms he shared with Kovalevsky died of it. Much depressed, the two started for Ischia, but Elie soon realised with terror that he was not yet well enough to work; in order to recover quickly, he went to Cava, a pretty little place, renowned for its salubrious climate.

There he met Bakounine again, and they saw a good deal of each other in a friendly way. Bakounine nicknamed him “Mamma” because of his almost maternal attentions, a nickname which, for the same reason, was given him later, quite independently, by other intimates. Yet, though their relations were cordial and even affectionate, there was not really much in common between the two. Elie thought Bakounine’s ideas superficial, and disliked his sectarian mentality; they ultimately drifted apart.

His health having gradually recovered owing to the rest, he returned to Naples in the autumn, after the epidemic had abated, and at last resumed his work.

Whilst studying the history of the development of Cephalopoda he found that they had embryonic layers similar to those of Vertebrates; this was the first time that the fact was established. It was extremely important, for it constituted a concrete and indisputable proof of the existence of a genetic connection between inferior and superior animals. Metchnikoff chose this subject for his thesis, and, having completed his researches, he returned to Russia in 1867.

By this time he had made great use of his three years’ stay abroad. Though he had not showed himself a docile pupil, yet he had become initiated into the organisation of scientific work in Germany; he had carried out independent researches and had been able to choose with full knowledge the future path of investigations which he was to pursue for many years in the field of Comparative Embryology.

Already the observations he had made had in themselves a real importance. For instance, his studies in divers specimens of the worm type, a type which offers very heterogeneous forms, had permitted him to establish links of continuity between certain groups among them. Whilst studying those animals at Giessen in 1865, he had discovered the capital fact which proved to be the starting-point of all his future work—the intercellular digestion of an inferior worm, a land planarian, the Geodesmus bilineatus. He had compared this digestion with that of the superior Infusoria and had seen in it one more proof of the genetic connection between the type of the Protozoa and that of worms.

He did not then realise the full bearing of this observation, which really constituted the basis of his future phagocyte theory; this was only to appear eighteen years later.

He had also made researches on numerous specimens of insects and on the scorpion, establishing the fact that they all had embryonic layers; he concluded that he was “entitled to extend the theory of embryonic layers to Arthropoda.”

Finally, he had discovered embryonic layers similar to those of the Vertebrates in inferior Invertebrates, the Cephalopoda (Sepiola). This established a link of continuity between the higher and lower animals.