238 PARASITISM 



some great disease wtive which in remote time swept 

 through the American Continent. Evidence of the 

 great antiquity of insect pests and parasites has 

 recently come to hght. Scudder describes the dis- 

 covery of a fossil African Glossina (tsetse fly), in tlie 

 American Miocene, a find whicli may go far to 

 exphiin the extinction of the -^Vmerican Kquidce. 

 lluffer, of Alexandria, has demonstrated the presence 

 of the common Egyptian parasite, Bilharzia luema- 

 tobia, in the tissues of munmiies of the 20th Dynasty, 

 1250-1000 E.G. 



AVhen it is fully grasped that the minute blood 

 organisms which give rise to malaria, probably also 

 to yellow fever, sleeping sickness, and other tropical 

 diseases, are animal parasites M'hicli thrive in the 

 tissues of higlier species, and that in order to do so 

 they must have adapted themselves to the ever- 

 changing hostile reactions of the tissues of their hosts 

 — (for the tissues of the unwilling hosts will have 

 naturally opposed every advance wliicli these parasites 

 will have made) — we can comprehend how capable 

 must be the protozoon of malaria, the trypanosome, 

 tlie filaria and the spirocha^te to adapt themselves 

 to the ever-varying tissue reactions, if they are to 

 enter our bodies and to surxive and multiply in our 

 tissues. 



It is truly marvellous how, for instance, the protozoon 

 of malaria lias not only adapted itself to its human 

 host, but lias also made itself at home in the body 

 of the nios(piito — an insect so widely separated from 

 man in the animal scale. 



