THE ADVANCE OF SCIENCE 135 



The remarkable development of Metschnikoff's doc- 

 trine of phagocytosis during the past quarter of a 

 century is certainly one of the characteristic features 

 of the activity of biological science in that period. 

 At first ridiculed as ' Metschnikoffism,' 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 condi- 

 tions which can thus be effected, yet we cannot hope for 

 any really complete or satisfactory 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 guarded activity, of 

 those wonderful colourless amoeba-like corpuscles whose 

 use was so long unrecognized, but has now been made 

 clear by the patiently continued experiments and argu- 

 ments 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 resis- 

 tance to infection. Of this kind were the beliefs that 

 the liquids of the living body have an inherent and some- 

 what vague power of resisting infective germs, and even 

 that the mere living quality of the tissues was in some un- 

 known way antagonistic to foreign intrusive disease-germs. 



