February 9, 1922] 



NATURE 



165 



the animal kingdom. Metchnikoff was convinced 



that in the case of such a fundamental mechanism 



that he had discovered in invertebrates this would 



rove to be true, and shortly afterwards he suc- 



jded in establishing the generality of the pheno- 



lon by experiments upon higher animals infected 



rith the anthrax bacillus. In this case the bacilli 



rere attacked and eaten by the white blood cor- 



iscles which wander everywhere. Two other 



)servations recorded deserve special mention be- 



luse they opened up new country, the exploration 



jf which occupied Metchnikoff and his pupils and 



jany others for the next twenty years. 



The first of these was that active phagocytosis 



:urred only in animals refractory to anthrax, thus 



)roviding a possible interpretation of the natural 



imunity of some species of animals to a disease. 



The second was that animals naturally sensitive to 



ithrax could be induced to respond like naturally 



jfractory ones by vaccination, an indication of the 



iture of acquired immunity. 



Such entirely new conceptions were not readily 



juiesced in, and even encountered hostility. Two 



reat men, Virchow and Pasteur, however, were 



lediately impressed by them, and in 1888 the 



itter invited Metchnikoff to come to the Pasteur 



stitute. The invitation was accepted, and there 



remained until the end of his life, occupied 



ider ideal conditions in developing the conse- 



lences of his discovery at Messina. 



At the Pasteur Institute he found every facility 



)r his researches, and was undisturbed by adminis- 



rative or academic work. He enjoyed the com- 



lionship of wise colleagues, themselves actively 



igaged in inquiries in bacteriology and pathology, 



id soon became surrounded by willing pupils ready 



undertake investigations dictated by his fertile 



lagination. 



This was a time of immense activity, mainly 

 roted to exploring the whole subject of 

 mnity which he had illuminated by the 

 liscovery of phagocytosis. This prolific period 

 of his career is skilfully dealt with in broad 

 outline, and details which, being of a highly 

 technical character, would be tiresome to the general 

 reader are omitted. The theories current regarding 

 immunity when Metchnikoff approached the subject 

 from a naturalist's point of view are briefly 

 sketched, and the influence of his work and that of 

 others in the development of our present views is 

 indicated. 



In 1900 Metchnikoff presented an account of his 

 researches to the International Congress of Medi- 

 cine at Paris, and fought his critics for the last 

 time. Then, convinced that his deductions were 

 sound, he proceeded to expound his views at length 

 NO. 2728, VOL. 109] 



under the title, " Immunity in Infectious Diseases," 

 which appeared a few years later. 



Metchnikoff 's greatest scientific achievement 

 was undoubtedly the discovery of phagocytosis 

 and its manifold significance in biology and 

 pathology, and it is clearly brought out in 

 his biography that he would not have made 

 these discoveries had it not been for his 

 previous training and research in zoology. Perhaps 

 the best way to appraise this, his contribution to 

 science, is to try to think what our present know- 

 ledge of inflammation and immunity would be with- 

 out it. 



At the age of fifty-three Metchnikoft" turned his 

 attention to the subject of senility. Regarded from 

 a long biological view, man's imperious instinct for 

 life in the later years of existence, notwithstand- 

 ing obvious breakdowns, must, he considered, be a 

 pathological coincidence. How, otherwise, was the 

 fear of death, a general and inevitable occurrence, 

 to be explained ? Metchnikoff imagined that this 

 lack of harmony exists because senility is premature 

 and partial and arrives before the natural instinct 

 for death has had time to develop. 



If this supposition were correct, the greatest of 

 life's disharmonies might be remedied, for be be- 

 lieved that it was within the power of science not 

 only to preserve the body from the depredations of 

 disease, but also to maintain the equilibrium of the 

 tissues. In such a case happiness and contentment 

 should be the lot of man for a period far exceeding 

 the usually allotted span. Upon such ideal physio- 

 logical existence or ' ' orthobiosis ' ' a quiet satiety 

 with living should, he supposed, ultimately super- 

 vene and death be welcomed as sleep at the end of 

 a long day. 



The consideration of the changes in the tissues in 

 old age led Metchnikoff to the conclusion that, 

 apart from the damage done by diseases such as 

 syphilis, tuberculosis, and other chronic infections, 

 the principal cause of premature degeneration of 

 the important cell elements was a prolonged in- 

 toxication by the products of the activities of the 

 innumerable bacteria which inhabit the large in- 

 testine. For this hypothesis he obtained anatomical 

 and experimental support. 



The former he tersely summarised by the phrase, 

 " the longer the large intestine, the shorter the 

 life," an aphorism which is to some extent respon- 

 sible for the depredations of some of our famous 

 surgeons. 



Having arrived at the conviction that unlicensed 

 bacterial activity in the colon was harmful, Metch- 

 nikoff essayed to control it by implanting into the 

 alimentary canal a special microbe which produced 

 much lactic acid from carbohydrates, and was itself 



G 



