446 the president's address. 



Then there are the relapsing fevers caused by spirochaetes in the 

 blood, and said to be transmitted in Europe by bed-bugs, but in 

 Africa by a species of tick which lives in mud floors. In India and 

 other parts of the Tropics we find that the deadly disease known 

 as kala azar, due to a parasite, is "transmitted in all probability 

 by bed-bugs. All these and many others furnish points of great 

 interest, but I must be content with the three examples with 

 which I have dealt in more detail, in order to show you how great 

 a work has been done and is being done in this field. As 

 Prof. Osier said recently, these discoveries are going to have 

 an enormous influence on the history of the world and of man- 

 kind, because they are going to make the Tropics habitable by 

 white men. We hear or read so often of such-and-such a country 

 being uninhabitable by Europeans on account of its deadly 

 climate ; but when we look into the matter we find that it is 

 not the climate at all that is to blame, but that the white races 

 -are killed off by diseases caused by some animal parasite with 

 which they are inoculated by the bite of some blood-thirsty 

 -arthropod. Take Uganda, for instance, with which I have a 

 slight acquaintance : all that the climate does for you there is 

 to give you a sunstroke if you go out in the heat of the day 

 with inadequate .headgear, and to make it very difficult to keep 

 awake after lunch. Some well-known European diseases, such 

 us small-pox and syphilis, are also rife there ; but on the other 

 hand, some of our familiar plagues, such as tuberculosis, rheumatic 

 fever, and influenza, appear to be absent. The diseases that are 

 really to be feared are all such as spring from bites of arthropods. 

 If you protect yourself from the mosquito you will not get 

 malaria ; avoid the tsetse-fly, which is very easily done, and 

 you are safe from sleeping sickness ; do not sleep on mud floors, 

 nor pitch your tent on old encampments, and relapsing fever will 

 not trouble you ; keep rats and fleas at a distance, and you are 

 safe from plague. With a little care and attention to surroundings 

 the European finds his life in the Tropics if anything more free 

 from disease than in our temperate but influenza-ridden, 

 palaearctic climate. 



In the foregoing remarks I have drawn attention more 

 particularly to the practical results of microscopy wedded to 

 sagacious experiment, and have tried to show how fertile in good 

 results this union has been, and promises still to be. But I 



