222 BERTHA VAN H. ANTHONY AND C. V. EKROTH 



BROTH '2 



The tests on the meat infusions were carried out before any 

 peptone or salt had been added. In the preparation of broth 

 the choice of titration methods must of course be governed by 

 the manner of preparing the meat juice in the preHminary steps. 

 The relative merits of pressing out the meat juice before or 

 after heating the soaked meat must be determined by experiment 

 in the kinds of work for which the media are destined. 



For those workers whose needs and experience lead them to 

 express the meat juice in the cold state and then dissolve the 

 peptone and salt with very little preliminary heating, the use 

 of the boiling titration for correction is essential, in order to 

 approximate the future conditions due to further heating and 

 sterilization after the reaction of the batch of medium has been set. 



In this laboratory the best toxin production has seemed to be 

 obtained when the meat juice is pressed out after heating large 

 amounts (20 liters) for one hour at 45° to 55°C. and then boil- 

 ing up strongly until the meat coagulates. The meat infusion^^ 

 is then strained through cheese-cloth. After the requisite 

 amount of peptone and salt have been dissolved by further heat- 

 ing up to the boiling point and the mixture boiled one half hour, 

 the reaction is set according to a room temperature titration. 



If the specimen is boiled'^ in the casserole before titration, 

 it no longer represents the lot of broth in the kettle but has 

 risen somewhat in acidity. Consequently, if the large lot be 

 adjusted according to the boiling titration a false correction 

 is made. To be sure, after adding the normal soda solution, 



^' Broth = meat infusion plus peptone and, usually, salt. 



'^ This method proves useful in other lines of work for at this point the in- 

 fusion can be filtered, sterilized and stored. It is ready for further use on the 

 addition of any suitable peptone and may be set at any desired reaction; or it 

 is ready as a basis for making agar. 



1^ At this point may be mentioned the length of time recommended for boil- 

 ing by different authors. Heinemann (1911) heats "to boiling." Jordan (1914) 

 MacNeal (1914) and the Standard Method (1913) boil one minute. Park and 

 Williams (1914) boil two minutes, Abbott (1915), Abel (1914), Hiss and Zinsser 

 (1914), Mallory and Wright (1915), Swithinbank and Newman (1903) boil for 

 three minutes. 



