2 12 THE CAUSATION OF DISEASE. 



is apt to inherit also the mental aptitude of the ancestor who 

 actually acquired it.* 



Seeing that scarcity of food is very rarely a direct cause of 

 premature death among civilized communities, let us now 

 inquire into those other conditions with which animal 

 organisms have to cope ? They are countless. Foremost 

 among them must be reckoned that long array of evils due to 

 insanitary conditions. We have also to take into account 

 peculiar atmospheric conditions, extremes of heat and cold, and 

 innumerable other injurious conditions. 



Such injurious external E's obtain frequently enough among 

 the lower animals, and are a fruitful source of disease in them, 

 wherefore it may be said that there is a perpetual struggle 

 against these conditions, those animals which are least capable 

 of withstanding their evil effects being weeded out, the " fitter " 

 surviving ; but injurious external E's are far less numerous 

 for the lower animals than for man, and, notably, civilized 

 man. The brutes are tied down to a comparatively limited 

 plan of action by a simple instinct. They are, in short, sur- 

 rounded by a comparatively simple environment, but as instinct 

 is replaced by the higher developments of mind the environ- 

 ment is rendered more and more complex, and disease-causing 

 agencies are multiplied a thousandfold. For, as mind evolves, the 

 social division of labour proceeds : we have this man following 

 one calling, that man another, till in a complex social com- 

 munity such occupations are to be reckoned by the thousand. 

 The environment of each of these, be it remembered, is dis. 

 tinct : it is distinct for the sweep, navvy, knife-grinder, butcher, 

 publican, acrobat, sempstress, actor, painter, lawyer, doctor, and 

 the countless other callings which help to build up the highly 

 complex fabric of civilization. Some of these occupations 

 are perfectly consistent with health, but many tend directly or 

 indirectly to excite disease, and a large volume might be written 

 on diseases peculiar to special callings. 



Again, there are many forms of mal-E in a civilized society 

 to which large numbers are exposed, independently of calling, 

 such as drink, sexual excess, damp dwellings, draughts, absence 



* These remarks do not apply so forcibly to individuals who inherit their 

 wealth by entail from a far-off ancestor. 



