132 EXAMINATION OF AIR, WATER, AND SOIL. 



by using sugar instead of sand. After the air has been 

 forced in at 6 the cotton plug is replaced and through the 

 large opening c, sterile gelatin is poured into the tube, which 

 dissolves the sugar ; and an Esmarch roll is made at e. 



Uffelmann found that in the open country 1 cubic meter 

 of air contains 250 germs ; on the seacoast, 100 ; in the court- 



FIG. 39. 



The Sedgwick-Tucker aerobioscope : a, brass wire gauze stopper ; c and b, cotton 

 stoppers ; d, sugar ; e, site for Esmarch roll. (Abbott.) 



yard of the University of Rostock, 450. The number was 

 less after a rainfall, and greater on a windy day. These find- 

 ings have been verified by others. 



It must be remembered, however, that most of these organ- 

 isms are not pathogenic. The number of bacteria found in 

 the air is of little clinical importance unless they are patho- 

 genic. 



Examination of Water. 



Water which contains even a trace of organic matter always 

 contains bacteria. Bacteria will not grow in water free from 

 organic matter, although they may remain alive in it for a con- 

 siderable time. The bacteria contained in water are usually 

 of the non -pathogenic variety. At times, however, both the 

 Bacillus typhosus and the spirillum of cholera may be found 

 in water. More bacteria are found in water after a rainfall 

 than before, because the rain has washed them out of the air 

 into the water. Warm water contains more bacteria than cold 

 water ; shallow water more than deep ; water at rest or having 

 only a sluggish current more than running water ; unfiltered 

 more than filtered water. Inasmuch as water plays such an 

 important part in the human economy, the bacteria which it 

 contains are of more than passing interest, and especially at 

 such times when the water-borne diseases are epidemic. 





