AIR, SOIL, AND WATER. 18? 



Agar and bouillon are used in qualitative analyses. A large 

 quantity of the water is taken (about 100 c. cm.) and mixed 

 with 25 c.c. of bouillon ; the mixture is then placed in an in- 

 cubator. The ordinary water-bacteria do not bear the higher 

 temperatures very well, and therefore pathogenic organisms 

 as cholera, for instance will be found almost in pure cultures. 



The growth of intestinal bacteria is also favored by glucose 

 bouillon (2 per cent.), and fermentation ensues. If a fermenta 

 tion-tube (Smith's) is used, the gas collects at one end, and the 

 bacteria can be further cultivated and studied. 



Varieties Found. The usual kinds found are non-patho- 

 genic, but, as is well known, typhoid and cholera are princi- 

 pally spread through drinking water, and many other germs 

 may find their way into the water. Some of the common 

 varieties give rise to fluorescence, or produce pigment. 



Eisenberg gives 100 different varieties as ordinarily found. 

 Other intestinal diseases also are supposed to be water borne, and 

 the presence of large numbers of the Bacillus coli communis is 

 strongly suggestive of sewage contamination. Ice supplies 

 require the same supervision as water supplies, for many bac- 

 teria, like the typhoid bacillus, retain their vitality for weeks 

 after freezing. 



The Examination of the Soil. The upper layers of the soil 

 contain a great many bacteria, but because of the difficulty in 

 analyzing the same, the results are neither accurate nor con- 

 stant. The principal trouble lies in the mixing of the earth 

 with the nutrient medium ; little particles of ground will cling 

 to the walls of the tube, or be imbedded in the gelatine, and 

 may contain within them myriads of bacteria. As with water, 

 the soil must be examined immediately or very soon after it is 

 collected, the bacteria rapidly multiplying in it. 



When the deeper layers are to be examined, some precautions 

 must be taken to avoid contamination with the other portions of 

 the soil. One method, very laborious and not often practical, ia 

 to dig a hole near the spot to be examined and take the earth 

 from the sides of this excavation. 



Fr'ankel's Borer. Frankel has devised a small apparatus in 

 the form of a borer, which contains near its lower end a small 



