:!7S H. B. Seddon : 



heeii used, the idea l)eiiig suggested by the " Nephelometer " of 

 MoFailaud (4). 



For the test the following solutions are made: — A 1% solution 

 of Barium chloride in distilled water, and a 1% solution of Sul- 

 phuric acid in Avater. Three cubic centimetres of the Barium solu- 

 tion is then mixed with 97 cubic centimeters of the acid solution, 

 shaken, and allowed to stand, to come to a state of chemical equi- 

 liliriuni. 



The B. abortus is sown on agar in Roux flasks and incubated 

 for two or three dajs, the water of condensation being ruti over 

 the surface daily so as to get a good growth over the whole sur- 

 face. Twenty cubic centimetres of carbolised saline (Ac. Carb. liq. 

 0.5. Sod. chlor. 0.85, water 100) is then added to the flasks and 

 the growth washed ott'. shaken thoroughly, and passed twice through 

 filter-paper. Dilutions of this suspension, or " emulsion," as it is 

 generally called, are then made with carbolised saline as folloAvs : — 

 1 c.c. of emulsion and 1 c.c. of carbolised solution; 1 c.c. of emul- 

 sion and 2 c.c. of carbolised saline; and so on up to 1 c.c. of emul- 

 sion and 10 c.c. of carbol saline. These suspensions are the fluids 

 ti) l>e compared with the barium sulphate mixture. 



To compare, the Barium sulphate mixture is thoroughly shaken 

 and a small tube of about 1 cm. calibre filled with the fluid, tlie 

 fluids to be tested being placed in similarly sized tubes and com- 

 parisons made over printed paper. This Barium suspension is 

 our standard of opacity for emulsion (Standard X). 



Supposing the tulje which approximates the opacity of 

 the Barium mixture is that tube which contains 1 c.c. of thick 

 emulsion and 6 c.c. of carbolised saline, then this tube is of the 

 proper standard, and is called "Standard X." The whole of the 

 ennilsion may then lie diluted down with rarltolised saline to the 

 proper strength, or kejjt as thick emulsion, the standard being* 

 now known. In the case instanced, the thick emulsion may be 

 termed " 7 X," thereby denoting that it requires diluting to seven 

 times its volume — i.e., adding six times its volume of carbolised 

 saline, to prepare a standardised enndsion "X." 



In our tests, in which we make the total volume of fluid in th© 

 tii})e up to 1.5 c.c, we use 0.5 c.c. of this standard emulsion " X " 

 in each tube. 



