Structure of the Bacteria. 11 



that these organisms are able to break clown such enor- 

 mous quantities of organic matter. Most of these en- 

 zyms react toward heat, cold and chemical poisons in a 

 manner quite similar to the living cells. In one respect 

 they are readily differentiated, and that is, that practically 

 all of them are capable of producing their characteristic 

 chemical transformations under anaesthetic conditions, as 

 in a saturated ether or chloroform atmosphere. 



Distribution Of bacteria. As bacteria possess greater 

 powers of resistance than most other forms of life, they are 

 to be found more widely distributed than any other type. 

 At the surface of the earth, where conditions permit of 

 their growth, they are found everywhere, except in the 

 healthy tissues of animals and plants. In the superficial 

 soil layers, they exist in myriads, as here they have abund- 

 ance of nourishment. At the depth of several feet how- 

 ever, they. diminish rapidly in numbers, and in the deeper 

 soil layers, from six to ten feet or moi\), they are not 

 present, because of the unsuitable growth conditions. 



The bacteria are found in the the air because of their de- 

 velopment in the soil below. They are unable to grow 

 even in a moist atmosphere, but are so readily dislodged 

 by wind currents that over land areas the lower strata of 

 the air always contain them. They are more numerous 

 in summer than in winter; city air contains larger num- 

 bers than country air. Wherever dried fecal matter is 

 present, as in barns, the air contains many forms. 



Water contains generally enough organic matter in so- 

 lution, so that certain types of bacterial life find favorable 

 growth conditions. Water in contact with the soil surface 

 takes up many impurities, and is of necessity rich in mi- 

 crobes. As the rain water percolates into the soil, it loses 



