president's ADDRESS; S^ 



characteristic features of the a-jtivity of biological science in that period. 

 At first ridiculed as ' Metschnikoffisni,' it has now won the support of its 

 former adversaries. 



For a long time the ideal of hygienists has been to preserve man from 

 all contact with the germs of infection, to destroy them and destroy the 

 animals conveying them, such as rats, mosquitoes and other flies. But it 

 has now been borne in upon us that, useful as such attempts are, and 

 great as is the improvement in human conditions which can thus be 

 effected, yet we cannot hope for any really complete or satibfactory 

 realisation of the ideal of escape from contact with infective germs. 

 The task is beyond human powers. The conviction has now been arrived 

 at that, whilst we must take every precaution to diminish infection, yet 

 our ultimate safety must come from within— namely, from the activity, 

 the trained, stimulated, and carefully guai'ded activity, of those wonder- 

 ful colourless amoeba-like corpuscles whose use was so long unrecognised, 

 but has now been made clear by the patiently continued experiments 

 and arguments of Metschnikoff, who has named them ' phagocytes.' 

 The doctrine of the activity and immense importance of these corpuscles 

 of the living body which form part of the all-pervading connective 

 tissues and float also in the blood, is in its nature and inception opposed 

 to what are called the ' humoral ' and ' vitalistic ' theories of resistance 

 to infection. Of this kind were the beliefs that the liquids of the living 

 body have an inherent and somewhat vague power of resisting infective 

 germs, and even that the mere living quality of the tissues was in some 

 unknown way antagonistic to foreign intrusive disease-germs. 



The first eighteen years of Metschnikoff's career, after his under- 

 graduate course, were devoted to zoological and embryological investiga- 

 tions. He discovered many important facts, such as the alternation of 

 generations in the parasitic worm of the frog's \\ing—Ascaris nigrovenosa — 

 and the history of the growth from the egg of sponges and medusa?. In 

 these latter researches he came into contact with the wonderfully active 

 cells, or living corpuscles, which in many low forms of life can be seen by 

 transparency in the living animal. He saw that these corpuscles (as was 

 indeed already known) resemble the well-known amoeba, and can take 

 into their soft substance (pi'otoplasm) at all parts of their surface any 

 minute particles and digest them, thus destroying them. In a trans- 

 parent water-flea Metschnikoflf saw these amoeba-like, colourless, floating 

 blood-corpuscles swallowing and digesting the spores of a parasitic fungus 

 which had attacked the water-fleas and was causing their death. He 

 came to the conclusion that this is the chief, if not the whole, value of 

 these corpuscles in higher as well as lower animai.-,, in all of which they 

 are very abundant. It was known that when a wound bringing in 

 foreign matter is inflicted on a vertebrate animal the blood-vessels become 

 gorged in the neighbourhood and the colourless corpuscles escape through 

 the walls of the vessels in crowds. Their business in so doing, Metschnikoff - 



showed,istoeatuptheforeign matter, and also to eat up and rornove the dead, 

 190G. D 



