362 THE WONDER OF LIFE 



a specific parasite of house-flies and their relatives, may 

 be useful as a check to the multipKcation of these 

 disease-distributors. One cannot help feehng that such 

 measures should be backed up by more evolved 

 cleanliness. 



Man has in great measure freed himself from the disgrace 

 of gaol-fever or typhus fever, the germs of which used to 

 be transmitted from man to man by the clothes-louse, 

 and he is in process of conquering other plagues, a 

 step in the conquest being, in every case, an investigation 

 of linkages. Every one knows how the minute animals 

 which cause malaria (Plasmodium) and sleeping-sickness 

 (Trypanosomes) are disseminated respectively by the 

 mosquito (Anopheles maculifennis) and the tse-tse fly 

 {Glossina pal/palis), and the human importance of these 

 four animals is beyond all estimation. 



A curious though perhaps imimportant fact concerning 

 a near relative of the Trypanosomes has been recently 

 reported, and may serve to illustrate possible complica- 

 tions. A species of Leptomonas was discovered by Lafont 

 in the latex of Euphorbia pilulifera in Mauritius, and this has 

 been confirmed by G. Bouet and E. Roubaud in regard to 

 other Euphorbias. They regard the infection as local 

 and temporary and without obvious pathological effects. 

 There seems httle doubt that the plant is infected through 

 the agency of a bug. 



That rats have to do with plague was perhaps referred 

 to in the Bible in the accoimt of an epidemic among the 

 Phihstines, which they connected apparently with ' the 

 mice that marred the land '. In more recent times, the 

 association of rat-mortaUty and human-mortaUty seems 

 to have been often remarked, and regarded as more than a 



