president's address. 35 



for that of ingestion of food particles into the cells we get the usuiil form 

 of digestion by juices secreted into a digestive cavity. Now this being 

 certainly the case in regard to the history of the original phagocytes 

 lining the polyp's gut, it does not seem at all unlikely, but on the con- 

 trary in a higher degree probable, that the phagocytes of the blood and 

 tissues should behave in the same way and pour out sensitisers and opso- 

 nins to paralyse and prepare their bacterial food. And the experiments 

 of Metschnikoff's pupils and followers show that this is undoubtedly the 

 case. Whether there is any great variety of and difference between 

 ' sensitisers ' and ' opsonins ' is a matter which is still the subject of 

 active experiment. Metschnikoff's conclusion, as recently stated in 

 regard to the whole progress of this subject, is that the phagocytes 

 in our bodies should be stimulated in their activity in order successfully 

 to fight the germs of infection. Alcohol, opium, and even quinine, hinder 

 the phagocytic action ; they should therefore be entirely eschewed or 

 used only with great caution whei-e their other and valuable properties 

 are urgently needed. It appears that the injection of blood-serum into 

 the tissues of animals causes an increase in the number and activity of tlio 

 phagocytes, and thus an increase in their resistance towards pathogenic 

 germs. Thus Durham (who was a pioneer in his observations on the 

 curious phenomena of the 'agglutination' of blood corpuscles in relation 

 to disease) was led to suggest the injection of sera during surgical 

 operations, and experiments recently quoted by Metschnikoff seem to 

 show that the suggestion was well founded. Both German and French 

 surgeons have employed the method with successful results, and the 

 demonstration that an immense number of microbes are thus taken up 

 and destroyed by the multiplication (due to their regular increase by 

 cell-division) of the phagocytes of the injected patient. After years of 

 opposition bravely met in the pure scientific spirit of renewed experiment 

 and demonstration, Metschnikoff is at last able to say that the foundation- 

 stone of the hygiene of the tissues — the thesis that our phagocytes are 

 our arms of defence against infective germs — has been generally accepted. 



Another feature of the progress of our knowledge of disease— as a 

 scientific problem — is the recent recognition that minute animal parasites 

 of that low degree of unicellular structure to which the name ' Protozoa ' is 

 given, are the causes of serious and ravaging diseases, and that the 

 minute algoid plants, the bacteria, are not alone in possession of tliis field 

 of activity. It was Laveran — a French medical man — who, just about 

 twenty-five years ago, discovered the minute animal organism in the red 

 blood-corpuscles, which is tlie cause of malaria. Year by year ever since 

 our knowledge of this terrible little parasite has increased. We now 

 know many similar to, but not identical with it, living in the blood of 

 birds, reptiles, and frogs. 



It is the groat merit of Major Ross, formerly of the Indian Army 

 Medical Staff, to have discovered, by most patient and persevering 

 experiment, that the malaria parasite passes a part of its life in the spot- 



D2 



