360 COLLECTED STUDIES IN IMMUNITY. 



THE MATERIAL EMPLOYED, AND ITS PREPARATION. 



In these experiments a great deal depends on the manner in which 

 the brain emulsion is prepared. We shall therefore again describe 

 the method in detail, although Wassermann and Takaki did so when 

 they reported their experiments. 



Each guinea-pig brain was thoroughly mixed with 10 cc. 0.85% 

 salt solution. In order to obtain uniform and good results it is neces- 

 sary that the emulsion be as fine as possible. For this purpose the 

 brain substance was crushed and the salt solution added, at first drop 

 by drop, until a fine uniform emulsion resulted. It is well instead of 

 using a mortar to use conical glasses, such as are employed at the 

 Rabies Inoculation Stations for preparing the fine cord emulsions for 

 injections. These conical glasses are about 10 cm. high and taper 

 not to a point, but to a hemispherical surface into which a ground- 

 glass pestle fits. 1 This very fine emulsion is then forced through 

 Herzberg funnels, such as are used in testing paper. If the emulsion 

 is forced through the finest of these, fitted with wire-gauze with the 

 smallest mesh obtainable, it will be found that the emulsion is actually 

 free from macroscopically coarse particles. 



The poison I employed was a tetanus toxin preserved in the 

 institute for diagnostic purposes. This poison, I may add, owing 

 to the special method of preparation, differed from Behring's test 

 poisons (at least from those which can be obtained in the market) 

 in being free from spores. This fact may perhaps not be without 

 significance, for, under the conditions which here obtain, a development 

 of the spores with consequent production of poison in the animal can- 

 not be denied offhand. 



This possibility must surely often be counted on. It was for this 

 reason that Ehrlich long ago allowed only such tetanus poisons as 

 were freed as much as possible from spores to be used for testing, 

 and for exact experimental studies. I shall soon publish an account 

 of the peculiarities of the procedure used in this institute for obtaining 

 such poisons, and also describe a method for preserving tetanus poison 

 permanently, which we have found very useful. 



The antitoxin used was also that preserved for testing purposes. 

 1 grm. contains 100 A. E. Behring. 



1 These can be obtained from F. and M. Lautenschlager, Berlin, N. 



