April 25, 1901] 



NA TURE 



621 



DR. 



METCHNIKOFF ON MICROBES AND 

 THE HUMAN BOD V. 



A SPECIAL meeting of the Manchester Literary and Philo- 

 •*^ sopical Society was held on Monday, April 22, when 

 Dr. Elie Metchnikoff, of the Pasteur Institute, Paris, delivered 

 the Wilde Lecture. Before the lecture, the president of the 

 Society (Prof. Lamb) presented the Wilde Medal for 1901 to 

 Dr. Metchnikoff, and the Wilde Premium for 1901 to Mr. 

 Thomas Thorp. 



Dr. Metchnikoff 's lecture, which was in French, was on " La 

 Flore microbienne du Corps humain." Dr. Metchnikoff ex- 

 plained that men were free from microbes at birth, but immedi- 

 ately after birth the surface of the skin and the mucous mem- 

 branes became peopled with them, and at the end of some days 

 they were numerous and varied. Their germs were derived 

 from the air, or from the water used in washing the child. In 

 summer they developed faster than in winter, and sometimes 

 within four hours after birth there would be found several 

 different sorts of microbes in the intestines. But as a rule their 

 appearance was first observed between the tenth and seven- 

 teenth hour after birth. The habitation preferred by the 

 microbes found in the skin was unquestionably, the capillary 

 follicles, a kind of deep sheath for the formation of hair. The 

 mucous membranes, the surface of which was always moist and 

 covered with substances by which microbes were readily nour- 

 ished, were generally supplied with them more abundantly thaYi 

 the skin. The conjunctiva of the eye, however, thanks to its 

 being continually washed by tears, usually rid itself of most of 

 the microbes that found their way into the eye either with the 

 fine dust in the air or through contact with the fingers. There 

 was no doubt that microbes penetrated into the very deepest 

 parts of the respiratory passages, though it was difficult to give 

 a precise account of those ordinarily inhabiting the windpipe, 

 the bronchial tubes and the lungs, since the presence of those 

 which are found there after death might be explained by the in- 

 trusion, after death, of microbes from adjacent organs of the body. 

 However that might be, the growth of microbes in the lower 

 respiratory passages ought never, in a healthy man, to be great. 

 It was the digestive organs that exhibited them in the greatest 

 abundance. Dr. Miller, of Berlin, had described more than 

 thirty species inhabiting the cavity of the human mouth, some 

 of them also to be found on the human skin ; others, which 

 were found about the teeth, were peculiar to the mouth and 

 were not met with anywhere else. Several of the species 

 characteristic of the mouth made their way deep into the diges- 

 tive organs and were recognisable in the stomach and the in- 

 testines. The stomach, with its acid contents, offered conditions 

 affecting in a quite exceptional way the development of micro- 

 scopic growths. Many kinds of bacteria could not endure an 

 acid environment; still, the bacterial system of the human 

 stomach was pretty rich, thirty different species having already 

 been distinguished, most of which were not found elsewhere in 

 the digestive system. In the stomach, and still more in the 

 small intestine, bacilli were the predominating form of microbe, 

 the number and relative proportions of microbes in the 

 small intestine varying with the food eaten. Meat 

 and vegetable diets re-pectively stimulated the develop- 

 ment of special bacterial form=, though even when the 

 diet was unaltered noteworthy fluctuations in the microbian 

 population were observable. From the smaller intestine 

 the microbes passed to the larger, where they were joined by a 

 great number of new kinds. Of all the parts of the human 

 body, the large intestine was undoubtedly the most abundantly 

 teeming with these growths. It was inhabited by about forty- 

 five species of microbe, chiefly bacteria, among which bacilli 

 were much the most numerous. The large intestine began to 

 be inhabited immediately after birth. Even on the first day of 

 life, before any food whatever had been taken, a fairly great 

 variety of microbes was to be found there. When the child was 

 suckled the population of the large intestine very soon under- 

 went a change. It became more uniform and was composed 

 mainly.and sometimes almost exclusively, of a particular bacillus. 

 In children fed with the bottle, on cow's milk, this bacillus was 

 found too, but in smaller numbers, the large intestine in these 

 children being much richer in microbes of various types. After 

 weaning, the abundance of microbes became much greater still. 

 The number of distinct species of microbes to be found in a man 

 in health could not be exactly estimated, but quite roughly and 

 provisionally might be put between sixty and seventy. 



What could one say of the function of these varied growths? 

 NO. 1643, VOL. 03! 



Among invertebrate animals there were some covered with 

 much more copious growths than were found on the humaa 

 skin. On the southern and western coasts of England there 

 was found in great numbers a kind of crab whose whole 

 shell was generally covered thickly with vegetable growths. 

 Their use was obvious. They assimilated the crab to the 

 marine vegetation, and made him invisible alike to his enemies 

 and to his prey. No such demonstration could be given of the 

 utility of the microbes on the human skin. On the other 

 hand, the flora of the cavity of the mouth might render man a 

 service. Everybody had noticed that wounds inside the mouth 

 healed much sooner than those on the outer skin. Moistened 

 by the saliva, the wounds remained in contact with the microbes 

 and their soluble products, which stimulated in a marked degree 

 the reaction of the human organism. The secretions of the 

 microbes attracted a great number of white blood-corpuscles, 

 which cleaned the wound, cleared it of microbes and mortified 

 tissues, and so favoured the process of recovery. In the lower 

 parts of the digestive system this function of microbes was 

 less important, the mucous membrane there being much more 

 seldom torn. But it was probable that the acids secreted by 

 many bacteria in the small intestine rendered a real service by 

 preventing the development of certain other microbes which 

 might impede digestion. This preventive function was mani- 

 fested also in the course of conflict between the human organism 

 and microbes of a \ ery dangerous kind, and there was reason 

 to believe that in some cases the germs of Asiatic cholera were 

 rendered innocuous by the action of the microbes which they 

 encountered in the intestines. It had also been contended by 

 some authorities that the microbes in the digestive system played 

 an important part in the digesting of food, and that without 

 them food could not be assimilated ; but the data available 

 would lead rather to the general conclusion that for the normal 

 action of the human digestion the presence of the intestinal 

 microbes was by no means indispensable. 



They should now try to ascertain whether the microbes in the 

 human system might injure its health. When the defensive 

 forces of the body flagged, whatever might be the reason, 

 the microbes on the skin began to multiply and to pour their 

 noxious products into the tissues and the blood. It often hap- 

 pened that serious boils and anthrax developed themselves in 

 persons suffering from diabetes or some other general disease, 

 their cause being, not the introduction of a morbid germ from 

 without, but the excessive multiplication of certain microbes 

 which are found in the healthy human skin and which now 

 took advantage of the enfeeblement of the defensive cells. But 

 the greatest harm was done by the microbes of the stomach 

 and intestines. It had been recognised that the gravity of the 

 danger incurred in cases of perforation of the intestines was 

 due to the inflammatory action of the microbes that escaped 

 into the peritoneum. Nor was the injurious effect restricted to 

 cases where the microbes penetrated directly into the other organs 

 or into the blood, for the microbes produced soluble substances 

 which could be absorbed through the wall of the intestines and so 

 make their way into the circulation. Several of these were 

 substances more or less poisonous in their action, and it was 

 very probable that a great many of these toxic products of our 

 intestinal flora had still to be ascertained. In spite of our 

 imperfect knowledge, there was reason to state, with the 

 greatest strength of conviction, that the poisons produced by 

 the intestinal microbes played a considerable part in causing 

 many and various maladies. Headaches, exhaustion, neuras- 

 thenia, dyspeptic asthma, certain forms of epilepsy, several 

 skin diseases, including acne, had by certain authorities been 

 attributed wholly or in part to the action of poisons originated 

 in the digestive system. Even in cases of mental disease its 

 importance could not be denied ; it had a noteworthy connec- 

 tion with diseases involving atrophy of the higher organs, such 

 as the brain, the heart, the kidneys and the liver. 



Dr. Metchnikoff then discussed at some length the relations 

 of the normal microbian population of the human body — that is, 

 the microbes present in it in a slate of health — and the patho- 

 logical microbes, or microbes directly inducing specific disease. 

 He pointed to the methods practised in medicine and surgery to 

 limit or counteract the action of microbes ascertainedly or 

 potentially generative of disease, and to what he believed to be 

 limitations to the beneficial operation of antiseptics. There was 

 a tendency to renounce more or less completely the use of anti- 

 septics, and to have recourse more and more to simply mechani- 

 cal measures for keeping microbes out of the body — the 

 prolonged washing of the hands, for instance, or the moistening 



