EXPERIMENTAL CONDITIONS 59 



the tube has been made into a suitable thoroughly 

 sterilised solution of a kind likely to favour their 

 growth and multiplication. 



The solution I have used for this purpose has 

 been one containing ten grains of neutral ammo- 

 nium tartrate and three of sodium phosphate to 

 each ounce of distilled water. Such a solution, 

 after it has been well boiled or superheated, 

 favours the growth of such organisms, though it 

 never engenders them. The mode of testing a 

 sample is, therefore, quite simple. Four or five 

 minims of the experimental solution with its de- 

 posit are dropped into a thoroughly sterilised 

 two-ounce flask containing some of the recently 

 reboiled test solution. 1 The flask is closed with 

 a freshly boiled india-rubber stopper, and is then 

 left in a warm chamber for from two to ten days 

 or longer. 



If Bacteria are plentiful, such a test solution 

 will become more or less turbid in the course of 

 from two to three days. Where Bacteria are less 

 abundant, or less prone to multiply in the solution, 



1 The flasks were sterilised by keeping them in a steriliser 

 such as is used for surgical instruments, or else by putting 

 them into an oven. In either case they were allowed to remain 

 for over an hour, and the heat was sufficient to render cotton- 

 wool slightly brown. 



