BACTERIA AS PLANTS. 39 



surface accumulations. Lakes or reservoirs, how- 

 ever, by standing quiet allow the bacteria to set- 

 tle to the bottom, and the water thus gets some- 

 what purified. They are in the air, especially in 

 regions of habitation. Their numbers are great- 

 est near the surface of the ground, and decrease 

 in the upper strata of stir. Anything which 

 tends to raise dust increases the number of bac- 

 teria in the air greatly, and the dust and emana- 

 tions from the clothes of people crowded in a 

 close room fill the air with bacteria in very great 

 numbers. They are found in excessive abun- 

 dance in every bit of decaying matter wherever it 

 may be. Manure heaps, dead bodies of animals, 

 decaying trees, filth and slime and muck every- 

 where are filled with them, for it is in such places 

 that they find their best nourishment. The bod- 

 ies of animals contain them in the mouth, stom- 

 ach, and intestine in great numbers, and this is, of 

 course, equally true of man. On the surface of 

 the body they cling in great quantity ; attached 

 to the clothes, under the finger nails, among the 

 hairs, in every possible crevice or hiding place in 

 the skin, and in all secretions. They do not, 

 however, occur in the tissues of a healthy indi- 

 vidual, either in the blood, muscle, gland, or any 

 other organ. Secretions, such as milk, urine, etc., 

 always contain them, however, since the bacteria 

 do exist in the ducts of the glands which conduct 

 the secretions to the exterior, and thus, while the 

 bacteria are never in the healthy gland itself, 

 they always succeed in contaminating the secre- 

 tion as it passes to the exterior. Not only higher 

 animals, but the lower animals also have their bod- 

 ies more or less covered with bacteria. Flies have 

 them on their feet, bees among their hairs, etc. 



