19 



culated the culture solutions could be prepared without the 

 measurement or less than 0.5 cc. in any case. Thus errors 

 that might have arisen in attempting to read hundredths of 

 a cubic centimetre on a burrette graduated only to tenths, 

 wern obviated. 



In making up a series of cultures the two salt sol- 

 utions which were to be combined were usually diluted to 

 twice the concentration finally desired and then placed in 

 burrettes. From these Tere prepared, with addition of water 

 as needed, the combinations and concentrations actually used 

 in the experiments. These mixtures, in volumes of IC cc. or 

 more, were made in small flasks (of about 75 cc. capacity), 

 a flask being provided for each of the different combinations 

 as well as one for the control. The latter solution contained 

 the salt of the heavy metal alone. 



From each of the flasks just mentioned a small por- 

 tion of solution (about a cubic centimeter) was placed in a 

 separate glass dish ( 2x3 cm.) to which spores from a 

 stock culture were then transfered. These inoculations were 

 made in order, beginning with the weakest solution of the 

 lighter metal. A platinum needle was used for this purpose, 

 flamed and washed to clean and sterilize it after each in- 

 oculation. 



In each case the tip of the needle was dipped a sin- 

 gle time in the well mixed mass of spores which had been pre- 

 pared as already described, and the spores which adhered were 

 washed off in the culture solution. Thus approximately the 

 same number of spores were inoculated into all of the dishes 



