APPENDIX 497 



From dilutions of i : 10,000 to i : 100,000 rise by increments 

 of 5000. 



From dilutions of i : 100,000 to i : 1,000,000 rise by increments 

 of 100,000. 



When dealing with a substance of unknown powers and this 

 is especially true with regard to agglutinating sera it is customary 

 to run a preliminary test, using a few widely separated dilutions 

 such as may be obtained in the following manner: 



FIRST DILUTION I. 



i c.c. serum + 9 c.c. normal saline solution = 10 per cent, 

 solution or i: 10 dilution (of which i c.c. contains o.i c.c. of the 

 original serum). 



When dealing with fluids other than serum the diluent is 

 usually distilled water; whilst if the original substance is a solid 

 the instructions would read : 



i gram o.s. + 10 c.c. distilled water = 10 per cent, solution, etc. 



SECOND DILUTION II. 



i c.c. first dilution + 9 c.c. normal saline solution = i per 

 cent, solution or 1:100 dilution. 



THIRD DILUTION III. 



i c.c. second dilution + 9 c.c. normal saline solution = i per 

 mille solution or i: 1000 dilution. 



FOURTH DILUTION IV. 



i c.c. second dilution + 9 c.c. normal saline solution = o. i per 

 mille solution or i : 10,000 dilution. 



The following tables showing the secondary dilutions that can 

 readily be prepared from each of these four primary dilutions for 

 use in the subsequent determination of the exact titre will probably 

 be found of service by those who are not ready mathematicians. 



