458 



is certain, however, that it is conveyed from one person to another 

 by a mosquito. A few interesting points in connection with the 

 mosquito and this disease are worth mentioning as showing how, 

 by analogy, in spite of the germ never having been found, we 

 may safely conclude that this is a protozoal disease, and that the 

 organism most probably undergoes a change similar to that 

 described for the malaria parasite : (1) Only mosquitoes which 

 are fed on a patient during the first three days of the disease 

 become infective that is, are able to transmit the disease to 

 another ; (2) not until the twelfth day after the mosquitoes have 

 fed on a sick person are these able to convey infection to a healthy 

 individual ; (3) such mosquitoes remain infective for at least fifty- 

 seven days. Consequently, it is most probable that the organism 

 undergoes a developmental process within the mosquitoes during 

 the twelve days mentioned, and that the mosquito does not act as 

 a mechanical transmitter, but as an intermediate host. Regard- 

 ing relapsing fever, an interesting fact has been proved namely, 

 that the spirochaete may pass from a pregnant female into the 

 egg, thence to the larva and to the adult, so that the progeny of 

 infective ticks may themselves be infective without having pre- 

 viously bitten an infected person. Sleeping sickness is met with 

 only in the Equatorial territories of the African continent, and, 

 although it is practically certain that it is endemic on the west 

 coast, it has slowly but surely crossed the Dark Continent, and 

 by numerous epidemics this ghastly and terrible disease has 

 destroyed whole villages in Central Africa with marvellous 

 rapidity. It is practically always fatal, and the white man is 

 equally susceptible with the black. It is caused by a protozoal 

 organism in the blood, which eventually implicates the nervous 

 system. The parasite is conveyed from the sick to the healthy 

 by a dipterous insect universally known as a *' tsetse." From the 

 commencement of the infection to the terminal stage, there is 

 reason to believe that in some cases an interval of years may 

 elapse, though probably in the majority the march of events is 

 much more rapid. 



It is an old adage that prevention is better than cure, and 

 enough has been said to indicate that in the subject under 

 discussion prevention must be sought for on the insect side. 

 These diseases can never be eradicated simply by medical treat- 

 ment, and so long as the carrier exists, so long will the disease 



