CHAPTER XX 1 

 A CLEAR MIND THE NEED OF THE DAY 



Every living being must contend with enemies for its own 

 existence. In the early periods man counted among his foes 

 wild animals, storms, floods, famines and droughts. Against 

 these he has in a large measure ceased to contend; he has 

 overcome wild animals, and with fires, houses and various 

 other devices can defend himself against the elements of 

 nature. It is due to the wonderful power of his mind that he 

 has been able to master these enemies, and it certainly be- 

 hooves him to keep this, his greatest treasure, in as efficient 

 condition as possible. 



Man is still engaged in a struggle for existence with certain 

 foes which his changed conditions have brought prominently 

 forward, and the struggle is all the more severe because he 

 does not always recognize his worst foes as foes at all. Among 

 the most dangerous of his remaining enemies is the micro- 

 scopic, parasitic germ. Doubtless, germs existed in the early 

 periods of man's existence, but they were not especially 

 serious until people came to live in crowded communities. 

 The larger the community the greater becomes the danger 

 from microbes. An epidemic may kill thousands and other 

 diseases, like tuberculosis, which do not produce violent 

 epidemics, are quietly at work destroying the lives of hundreds 

 of thousands each year. Germs are particularly dangerous 

 because they are invisible, because people do not know where 

 they are nor how to avoid them, and because they are capable 

 of multiplying so fast that no matter how many of them are 

 destroyed, their numbers can in a few days be fully replaced 

 1 This chapter is entirely the work of the senior author. 

 328 



