EXAMINATION OF AIR, SOIL, AND WATER 2IQ 



Sand is sterilized by heating to redness, and while still 

 warm placed in test-tubes, which are then plugged. (Sand 

 which has been passed through a sieve with meshes 0.25 mm. 

 wide is the kind required.) A glass tube 9 cm. long is provided 

 with two portions of sand, each 3 cm. long and J cm. apart, 

 little plates of brass gauze keeping the portions in position. 



The tube and its contents are now sterilized in a hot-air oven 

 at 150 C., the ends having first been plugged with cotton. 



One end of the tube is then fitted with a rubber cork through 

 which passes a glass tube, which is connected with an aspirator 

 (a hand-pump with a known capacity) . 



If a 100 liters of air pass through the tube in fifteen min- 

 utes, the germs should all be arrested in the first sand-filter. 

 And when the filters are removed and thoroughly mixed with 

 gelatin, each filter for itself, there should be no colonies devel- 

 oped from the second filter, i. e., the one nearest the aspirator. 



Sedgwick-Tucker Method. A special form of tube is used, 

 called an aerobioscope. It consists of a neck 2.5 cm. in length, 

 an expanded portion 15 cm. long, and a long narrow tube of 15 

 cm. After sterilization the tube is partly filled with granulated 

 sugar, which is the filtering material. By means of a vacuum 

 gage and an air-pump, or ordinary aspirating bottles, the vol- 

 ume of air passing through the apparatus can be determined. 

 After the air has been passed through, the sugar is gently 

 shaken from the narrow tube into the expanded portion, and 

 20 c.c. of liquefied gelatin is poured in. The sugar dissolves, 

 and the mixture is then rolled on the inner side of the glass 

 as an Esmarch tube. This part of the apparatus is divided into 

 squares to make the counting of colonies easy. The aerobio- 

 scope is very highly recommended. 



Varieties Found in Air. The only pathogenic bacteria 

 found with any constancy are the Staphylococcus aureus and 

 citreus; but any bacterium can, through accident, be lifted into 

 the atmosphere, and in certain places may be always found 

 the Bacillus tuberculosis, for example, in rooms where many 

 consumptives are living. 



Typhoid fever, influenza, pneumonia, and diphtheria may be 



