164 NINETEENTH REPORT. 



In the studies of Shive and Tottingham the cultures were made up 

 with distilled water and pure cliemicals. We have repeated this work 

 with close agreement to their results. The work has been further ex- 

 tended to include studies of the physiological balance in soil solution, in 

 sand cultures and in soil cultures. Some of the main points in our studies 

 on the physiological balance in soil solutions are to be reported here. 



The soil solution used in these studies was obtained from selected 

 samples of soil by the oil pressure method devised by Dr. van Suchtelin 

 and more recently perfected and extended in its usefulness by Mr. 

 Morgan, of tlie Bacteriological Laboratory, Michigan Agricultural 

 College. 



The stock solutions of the three salts were made up separately in^ 

 concentration using the soil solution instead of distilled water as is the 

 usual custom. A fourth-molecular solution was selected since at this 

 dilution no precipitate appears for the period that the stock solutions 

 are needed. Oven dried salts were used. The bottles containing the 

 stock solutions wei'e fitted up with the necessary- burettes, glass and 

 rubber tubing to facilitate the tedious operation of making a culture 

 solution. The method was as follows : 



A 250 cc. volumetric flask was filled about two-thirds full of soil solu- 

 tion, then to this was added separately with frequent shaking, the various 

 amounts of the stock solutions as required. The flask was then filled up 

 to the mark with soil solution. The three salts were added so as to make 

 up a concentration of 1.7o atmospheres of pressure or about .4%. The 

 soil solution had a pressure of .220 so that the total concentration was 

 1.97, approximately 2. atmosplieres. This final concentration was 

 determined by the cryoscoi)ic method. In a series of solutions having 

 three constituents tlie relative proportion of these three salts may be 

 varied to give a great number of solutions, and still the total concentra- 

 tion will remain the same. In this jDarticular case the variation in the 

 proportion of salts was by increments of one-tenth the total concentration. 

 All the possible combinations would give a series of thirty-six cultures. 



These cultures fill tlie requirements necessary ; first they are all at the 

 same total osmotic concentration, second, the ratios of salts in every 

 culture differs from tlie others by increment of one-tenth the total concen- 

 tration, third, eacli culture solution contains the essential elements. Under 

 such conditions it would seem ])ossible to find the one best culture or 

 optimum physiological balance. 



The soil solutions obtained from various soils by the oil pressure 

 method show characteristic differences when considered from physical. 



"Morgan. .1. K. — The soil solution ohtjiim-d l)\ flic oil picssmc metliod. Soil Scienoc, 

 Vol. Ill, No. 0; 531-5t(i. nil 7. 



