no Chapters in Modern Botany CHAP. 



abundant laurels of discovery must be awarded discovered 

 this living dust, a knowledge of which has not only changed 

 some of our biological conceptions and created the dominant 

 school of medical theorists, but reformed and rationalised 

 surgery and hygiene, and exercised a potent influence 

 upon the greatest industries. To what is the importance 

 of bacteria due? They are very minute, quite invisible 

 individually to our unaided eyes minute spheres, rods, or 

 spirals they are, the smallest unit masses of living matter. 

 The secret of their strength is in their power of multipli- 

 cation. By repeated division and redi vision one soon 

 becomes a thousand ; indeed, given sufficient food, in a few 

 hours a single unit may have become the progenitor of 

 millions. 



But their importance depends also on their universal 

 distribution. Universal, indeed, for they live in the air 

 and in the soil, in food and raiment, in man, in beast, in 

 plant ; not even the water which we drink is free from 

 them. From the mouths of men to the walls of their 

 houses and the flies on the windows, from the hair of the 

 head to the toes of the feet, from the highway dust to the 

 recesses of the forest, and from wayside pool to sea, bac- 

 teria abound. But while they spread here, there, and 

 everywhere, they become most obvious wherever dead 

 organic matter is abundant, as in the refuse of our towns, 

 or in dead plants and animals. Rancid butter and rotten 

 cheese, " high " game-flavoured meats and over-stale bread, 

 blue milk and soured wine, as well as cesspools and dust- 

 heaps, sewers and slums, are their common habitats. 



Most important, however, is the fact expressed in the 

 "germ-theory," that bacteria are constantly and intimately 

 associated with some of the most fatal of human diseases, 

 such as consumption, diphtheria, smallpox or typhoid, 

 malaria or leprosy. Bacteria, in fact, kill most of us. 



