2;o EPIDEMIC AND ENDEMIC DISEASE 



abundance of others. Our many and vast English cities are 

 possible only because our peace is more profound and our means 

 of communication more perfect than ever before in the history of 

 man. On our tables may be found fruit and spices from the 

 tropics, wheat from Canada, Australia, and Russia, mutton from 

 New Zealand, beef from the Argentine, rice from India and China, 

 bacon from the United States, and fish from half the world. 

 To-day we may eat cheese or drink wine that has been stored for 

 years. So widely do we travel that there is on earth scarcely a 

 distinct language but some Englishman is able to express himself 

 in it. 



446. The pressure of population, therefore, is usually greatest 

 amongst the lowest types of mankind, and this results, not in 

 intercommunication, but in isolation ; in wars the object of which 

 is extermination not subjugation ; in a search for food, not for 

 slaves, whom a stone or pointed stick would arm as well as their 

 masters. Doubtless it was during this time of great pressure and 

 desperate struggle that man, spreading slowly from a common 

 centre, populated the Eastern and ultimately the Western 

 Hemisphere. 



447. The era of the early hunters, who subsisted solely on 

 wild animals and vegetables, was followed by that of the primitive 

 shepherds and husbandmen, who made provision, not only for the 

 immediate present by hunting, but for the future by labour. The 

 supply of food became more abundant and secure. Property in 

 land tended to become personal instead of tribal. Men began to 

 gather for mutual protection into communities, which differed 

 from one another in their stored productions. Barter, and there- 

 fore intercommunication, become more general and widespread. 

 Since the labour of a man now produced more food than sufficed 

 for his own existence, warfare underwent gradual change. The 

 conquerors sought slaves and tributaries rather than mere elbow- 

 room. They subjugated rather than exterminated their enemies. 

 Population increased immensely, and with it the microbes of 

 disease, which, spreading'.from their centre of origin, ranged to and 

 fro with travellers and raiders. 



448. The microbes of contagious diseases pass directly from 

 one individual to another. The living body furnishes their entire 

 environment, and, therefore, they are able to exist in all climates 

 and under all conditions. The long duration in the individual of 

 syphilis, the chief of them, makes itespecially capable of infecting and 

 maintaining its hold on new communities. But the method by which 



