49 6 



APPENDIX 



Percentage Formula for addition of salts, etc., to completed 

 media. 



Formula for preparing any desired percentage of a given salt, 

 etc., in tubed media; e. g., to make 4 per cent, solution of KNO 3 

 in a series of tubes of broth each containing 10 c.c. of medium, 

 when there is already available a 25 per cent, stock aqueous 

 solution of potassium nitrate. 



(AT+X) Y^A (X) 



IOO IOO 



N = number of cubic centimetres contained in each tube. 

 X = amount of stock solution to be added to each tube. 

 Y = percentage required in the medium. 

 A = percentage of stock solution. 

 Then 



(ip + X) 4^5X 



IOO IOO 



Therefore, 



Therefore, 



X= i . 9 c.c. 

 This allows for solution added to the original bulk of medium. 



Therefore, 10 c.c. broth +1.9 c.c. of a 25 per cent, aqueous 

 solution KNO 3 makes 11.9 c.c. medium containing 4 per cent. 

 KN0 3 . 



TABLES FOR PREPARING DILUTIONS 



(of Serum, Disinfectants or other substances.) 

 In estimating the agglutinin content or litre of a serum, 

 testing disinfectants and for many other purposes, it becomes 

 necessary to prepare a series of dilutions of the material under 

 examination, and in order to avoid unnecessary expenditure of 

 labour it is convenient to adhere to some definite scale of incre- 

 ment, such for example as the following : 



10 to 



From dilutions of i : 



of 5- 



From dilutions of i : 

 of 10. 



From dilutions of i . 

 of 25. 



From dilutions of i : 

 of 50. 



From dilutions of i : 

 of TOO. 



From dilutions of i : 

 of 250. 



From dilutions of i : 

 of 1000. 



80 to i 



200 to i : 



400 to 



500 to i 



1000 to i : 



5000 to i 



80 rise by increments 

 200 rise by increments 

 400 rise by increments 

 500 rise by increments 

 1000 rise by increments 

 5000 rise by increments 

 10,000 rise by increments 



