2;6 EPIDEMIC AND ENDEMIC DISEASE 



numerous but resistant, and where, therefore, the disease is endemic. 

 Rinderpest is said always to start from Southern or Central Asia. 1 



458. In histories and poems dealing with recent times, and in 

 the works of modern philosophers or people who attempt to found 

 new religious sects, we rarely meet any mention of endemic diseases. 

 These are accepted as part of the normal environment, and claim 

 allusion only when some prominent person dies of a ' decline ' 

 (consumption) or the like. But should a great pestilence occur, it 

 is eagerly noted, described, and made the basis of endless disserta- 

 tions and exhortations. Yet among modern civilised people 

 endemic disease claims by far the greater number of victims. So 

 also ancient records, which were written not for us but for the 

 contemporaries of the writers, tell as little of the endemic diseases 

 prevalent at the time as they do of the everyday life of the people, 

 but much of such great and striking disasters as epidemics and 

 wars. We may be sure, however, that some endemic diseases, for 

 example leprosy, the contagious maladies, and malaria, did exist 

 very anciently. 



459. A notable contrast between ancient and modern times is 

 furnished by the fact that pestilence (i.e. epidemic disease) was 



1 The microbic or other diseases of plants and lower animals, considered from 

 the standpoint of the student of evolution, constitute a vast subject of great 

 intellectual fascination and practical importance, which, it is to be hoped, some 

 worker with more time and knowledge than I am able to claim will investigate. 

 Like me, he will find his materials scattered through books of travel, histories, 

 and technical works, but will have to surmount even greater difficulties than I 

 have encountered in my very imperfect and fragmentary study of human disease. 

 Many profitable industries have been ruined or are being checked in various 

 parts of the world by plant or animal disease. Thus Phylloxera vastatrix (a species 

 of Aphides) caused great damage to the vines of France, and coffee-growing had 

 to be abandoned in Ceylon. Pig and poultry farming on a large scale are un- 

 profitable, because as surely as many animals are gathered in one place they are 

 swept by epidemic disease. Wild animals are delicate in captivity, mainly because 

 they perish of microbic diseases against which domesticated animals have under- 

 gone some evolution. The difficulties of the farmer illustrate very vividly the 

 dangers which beset the human race in its earliest struggles towards settlement 

 and civilization. Human selective breeding is at present outside the range 

 of practical politics. Selective plant and animal breeding is practised all the world 

 over ; but I am not aware that plants and animals, especially animals, have ever 

 been bred to any considerable extent with the view of increasing their powers of 

 resisting disease. Some horses and cattle, for example, are able to acquire im- 

 munity to the fly disease of Africa. Artificial selection achieves results much more 

 rapidly than Natural Selection. It should not be difficult to establish a resistant 

 race by continued breeding from animals that had shown themselves capable of 

 recovery from infection. Since plants are almost incapable of making use- 

 acquirements, and since their diseases are usually caused by muticellular organisms, 

 only ' inborn ' immunity could be evolved amongst them. 



