PRESIDENTIAL ADDRESS. 9 



appearance of the increased quantities of opsonins as 

 above, the phagocytes may be seen under the microscope 

 to have devoured many more than the same phagocytes 

 devour in blood in which the opsonins are not present to 

 the same extent. In this way it is now easy to measure 

 the degree of success with which the phagocytes in any 

 particular patient's blood are prepared to cope with this 

 or that kind of microbe by devouring them. The 

 opsonins have not been isolated, we do not know what 

 they are. What we know is their effects. The results 

 already obtained are so favourable that opsonin depart- 

 ments have been opened in many European and American 

 hospitals. It is now proposed to open such a department 

 at the Royal Prince Alfred Hospital. 



The Study of Tropical Diseases.— The results of the 

 definite study of tropical diseases constitute one of the most 

 remarkable achievements of medical science, and it is a 

 matter of only the last few years. Naturally, with our 

 numerous colonies and dependencies in tropical lands, the 

 study of these diseases is of the greatest consequence to 

 us as citizens of the Empire, for it is malaria that renders 

 or has rendered uninhabitable so many of what would other- 

 wise be the fairest parts of the earth. Whenever a tropical 

 country is said to be " unhealthy," one may take it that it 

 means malaria. In India malaria is said to kill twice as 

 many people as all other epidemic diseases put together. 

 In Italy it keeps five million acres uncultivated, and so on 

 and so on. Happily, however, no other disease has been 

 more thoroughly studied during the past decade, nor with 

 happier results, for great tracts of the earth's surface have 

 been rendered habitable which before were only fit for 

 wild beasts of sorts. And thus the political and economic 

 aspect of the study is most important. 



Until recently the mere high temperature of tropical 

 lands was held to be the cause of the enormous mortality, 



