80 



Dr. A. C. Kankin, 



[June 12, 



The medium used was plain nutrient agar, and the plates were incubated 

 at 37° C. In the later experiments a medium containing iron, esculin 

 and taurocholate of sodium, such as has recently been described by 

 Prof. Harrison, was used. B. coli were added to the water drawn from the 

 tap, so that the number of organisms very greatly exceeded that found 

 usually in contaminated water. 



A tube 40 cm. long by 3'5 cm. in diameter was drawn out to a nipple at 

 one end. Over this was fitted a piece of rubber tubing with a section of 

 glass tubing fitted on to the rubber at its distal end (see figure). The rubber 

 was of such length that it was possible to attach the smaller tube to the 

 side of the large one. The small tube extended above the level of the large 

 one, and was, when sterile, plugged with cotton wool. The whole 

 was then relatively sterilised by passing water at 70° C. through it 

 for one hour. The metal having been previously cleaned and 

 thoroughly washed in running water was dropped into the tube by 

 the unsterile hand; 155 c.c. of the inoculated tap water was then 

 added, and the apparatus attached to a Sprengel pump, and air 

 bubbled through the water for a period of one hour. At the end of 

 that time the rubber at the base of the large tube was pinched with 

 the fingers, the attachment to the Sprengel pump disconnected, and 

 a quantity of water removed from the larger tube by means of a 

 sterile pipette, plated on agar, 1/20 c.c. in each case, and incubated 

 at 37° C. for 24 hours, when the plates were examined and compared 

 with plates to which a similar quantity of tlie untreated inoculated 

 water had been previously added. In the tables these are referred 

 to as Plate 2 and Plate 1 respectively. For determining the amount 

 of peroxide of hydrogen present Bach's test was employed, as well as 

 the potassium iodide test. 

 Control Experiment. — Using the above technique, inoculated water, con- 

 taining B. coli, was bubbled for a period of one hour without the addition of 

 any metal. There was slight, if any, reduction in the number of organisms 

 in the water. Tlie siiui)lo bubbling of air for one hour through water 

 containing B. coli, then, does not cause any noticeable reduction in the 

 number of organisms present in the water. 



Effects of Metal without " BiiMling." — The following experin)ents were 

 performed to see what effects metallic aluminium, zinc, and copper had upon 

 l)acteria when placed in contact with water at rest containing B. coli in the 

 apparatus described. Hh; results are shown lielow. It will be observed that 

 zinc exerts some effect upon B. coli in one hour. It is noteworthy that 

 aluminium and copper exerted none : — 



