JiiL-sr 3, 1908] 



SCIENCE 



29 



bottom of eacli is a layer of nutrient gelatin; 

 and the tubing is adjusted so that a measured 

 volume of air may be drawn through the two 

 bottles in succession, by the action of a water- 

 suction bottle, shown inverted on the right of 

 the figure. In practise I place any desired 

 amount of water, generally one liter, in the 

 suction bottle and by slowly inverting it draw 

 a corresponding volume of air from the bottom 

 of the second culture bottle. The same vol- 

 ume of air passes from the bottom of the first 

 bottle into the top of the second and from the 

 outer air into the top of the first bottle. A 

 known amount of air is thus drawn into the 

 first bottle and the bacteria present settle out 



and form colonies on the gelatin. The volume 

 of air examined being less than the capacity 

 of either bottle, most of the bacteria remain 

 in the fijst. A few, which are carried down 

 by direct short currents, are caught in the 

 second bottle. The results of a few exam- 

 inations made by this method are shown in 

 the table below. 



The number of bacteria reaching the second 

 bottle is evidently small, in most cases less 

 than 10 per cent., and the number lost by 

 being drawn through the second bottle must 

 be negligible. With the exception of the pos- 

 sibility that bacteria may settle on the walls 

 of the bottles, the method should give a com- 



ATR EXAMINATION BY CULTUEE BOTTLE METHOD 



plete account of all bacteria present which 

 will grow under ordinary conditions of cul- 

 tivation. 



The culture-bottle method was devised pri- 

 marily as a check on the sand filter method; 

 and two types of sand filters were used for 

 comparison. The first was the classic Sedg- 

 wick-Tucker apparatus, which consists of a 

 glass tube 15 cm. long and 4 cm. in diameter, 

 opening at one end into a smaller tube 10 cm. 

 long and .5 cm. in diameter. A layer of 5 cm. 

 of sand was supported in the small tube by 

 wire gauze. A measured amount of air was 

 drawn through, entering the larger tube and 

 passing out through the sand. The sand, with 

 the bacteria filtered out, was shaken down into 

 the large tube, melted gelatin was added, and 



