64 LON A. HAWKINS 



each other and on the germinating spores might be considerably altered 

 if nutrient salts were present in the solution. In view of these considera- 

 tions these experiments were carried out without the use of nutrient media. 



METHODS. 



The salts used in these experiments were " Baker's analysed " chemicals, 

 procured in the original packages. Stock solutions of the different salts, 

 from which the experimental solutions were afterwards prepared, were 

 made up in o.2m, 14 o.5m, or molecular concentration. In preparing the 

 stock solutions the salts were weighed in glass-stoppered weighing bottles 

 directly from freshly opened packages and were dissolved in volumetric 

 flasks. These solutions were then made up to the required volume at a 

 temperature of 15 C. They were stored in Jena glass bottles which had 

 been carefully washed with saturated solution of potassium dichromate in 

 sulphuric acid, steamed for half a day, again washed with distilled water 

 and finally allowed to soak in distilled water for a month or more, to 

 remove any soluble matter which might be present. Distilled water from 

 a still with tin lined boiler and condenser was used in making the stock 

 solutions as well as in diluting them for the cultural work. Preliminary 

 tests showed that the spores germinated as well in water from this still 

 as in more nearly pure water distilled from potassium permanganate solu- 

 tion, using a hard glass flask and a block tin condenser. 



The stock salt solutions were diluted to the concentrations required in 

 making up the solutions for the experiments, by pipetting out the proper 

 amount into a hard glass beaker and then adding the necessary distilled 

 water from a burette. The concentrations of these solutions were so cal- 

 culated that the culture solutions could be prepared without the measure- 

 ment of less than 0.5 cc. in any case. Thus, errors that might have arisen 

 in attempting to read hundredths of a cubic centimeter on a burette gradu- 

 ated only to tenths, were obviated. 



In making up a series of cultures, the two salt solutions which were to 

 be combined were separately diluted to twice the concentration finally 

 desired, and were then placed in burettes. From these were prepared, with 

 addition of water as needed, the combinations and concentrations actually 

 used in the experiments. These mixtures, in volumes of 10 cc. or more, 

 were made in small flasks (of about 75 cc. capacity), a flask being pro- 

 vided for each of the different combinations as well as one for the control. 

 The latter solution usually contained the salt of the heavy metal alone. 



From each of the flasks just mentioned a small portion of solution (about 



14 The letter nt is used throughout this paper to denote molecular, a concentration of a single gram 

 molecule in a liter of solution. There seems to be considerable confusion in this important matter of 

 defining solutions, some chemists employing the letter n to denote molecular, although the latter has 

 long been used to denote chemically equivalent. 



