88 "COEFFICIENT OF DIFFUSION OF CELLS" 



units of the several factors, but also convenient standard 

 solutions of them. It is useful to keep this list ready 

 to hand in the laboratory. 



Alkali (sodium bicarbonate) increases diffusion. 

 Unit 0.005 gramme. Standard solution 5 per cent, 

 unity being 0.1 cc. It is convenient to remember 

 that this solution is neutralised by a 4. 175-per-cent 

 solution of citric acid, and that 1 unit of alkali is 

 neutralised by . 1 cc. of such a solution. Since the 

 agar at the outset is acid to the extent of . 083 gramme 

 to 50 cc., a tube of 10 cc., made up as described, must 

 contain . 0083 gramme of acid. This is exactly neutral- 

 ised by 0.2 cc. of the standard alkali solution; that is, 

 the agar at the outset, before any stain or other factor 

 is added, delays diffusion to the extent of 2 units. 

 Or, the addition of 2 units of sodium bicarbonate 

 will render the agar neutral. 



Sodium Citrate delays diffusion. Unit . 03 gramme. 

 Standard solution 10 per cent, 0.3 cc. being unity. 

 Since 50 cc. of agar contains 1 gramme at the outset, 

 the 10 cc. of jelly may be said to contain about 3 units. 



Sodium Chloride delays diffusion. Unit . 08 gramme. 

 Standard solution 10 per cent, unity being 0.8 cc. The 

 10 cc. of jelly contains this from the outset. 



Heat hastens diffusion. Each unit 5 C. ; 10 C. is 

 unity, 15 C. is 2 units, 20 C. 3 units, etc. For 

 practical purposes I call 37 C. 7 units. 



Time increases diffusion. Ten minutes is 1 unit, 

 twentv minutes 2 units, and so on. 



