100 



Mr. H. C. Ross. On a Coefficient of [Dec. 9, 



Convenient Method of Preparing the 10 c.c. of Jelly. — I have found it more 

 accurate and simple if the factors which hasten or delay diffusion are added 

 to the jelly from standard solutions, and I make the tubes of 10 c.c. of jelly 

 as follows : — 50 c.c. of a 2-per-cent. solution of powdered agar in water, 

 filtered and sterilised, is prepared. This solution has such a consistency that 

 another 50 c.c. of water could be added to it without preventing it from 

 setting on a slide when cold. 



Since I have shown that blood cells will not live on agar jelly unless it 

 contains a combination of sodium citrate and sodium chloride (3, 7), I add to 

 the 50 c.c. of jelly 1 gramme of sodium citrate and - 8 gramme of sodium 

 chloride, and accurately neutralise to litmus with citric acid. The whole is 

 then rendered acid by the addition of 0*083 gramme of citric acid. The 

 reason for this will be given in the next paragraph but one. 



The molten jelly is then decanted into test-tubes, each of which contains 

 5 c.c, so that it is possible to add the stain and certain quantities of the 

 standard solutions which contain the factors to these tubes, and provided the 

 total quantities of the several solutions added do not cause a tube to contain 

 more than 10 c.c. of jelly, its ultimate setting on a slide is assured. The 

 standard solutions are so arranged that their total quantity required in an 

 experiment never does exceed 5 c.c. On the other hand, if the amount is 

 less than 5 c.c, the balance up to the maximum in the tube of 10 c.c is 

 made up with water. In other words, a test-tube originally contains 5 c.c. of 

 jelly which is acid and holds a certain quantity of salts in solution. The 

 stain and quantities of the standard solutions, which correspond to the 

 number of units of factors which it is intended to try, are added. The total 

 content of the tube is then made up with water to 10 c.c. and boiled. So 

 that a test-tube never contains more nor less than 10 c.c. of jelly when a film 

 is prepared from it, though it may contain a variety of units of stain and 

 standard solutions. 



I have stated that the agar is rendered acid at the outset ; this is done to 

 reduce the number of factors. Acids and alkalies delay and accelerate 

 diffusion respectively. Since they neutralise each other, the neutral point 

 would also have to be taken into consideration. As this would complicate 

 the equation, I render the agar acid at the outset, so acid that I cannot get 

 any cell to stain on it with 1 unit of stain, and deal only with alkali. The 

 neutral point I ignore, although by knowing the initial acidity of the agar, 

 and that the units of all the factors are equal, the point can be readily 

 determined by referring to the equation. I therefore deal with one factor, 

 alkali, instead of two and a neutral point. 



To recapitulate shortly : 50 c.c of a 2-per-cent. solution of agar is prepared 



