MARKET COLD-STORAGE CHICKENS. 75 



BACTERIOLOGICAL STUDIES. 

 TECHNIQUE. a 



The aim of the work having been to study not only qualitatively, 

 but also quantitatively, the organisms found in the flesh of chickens, 

 it was necessary to develop methods which would be available for 

 the study of both phases of the subject. Since the number of organ- 

 isms in the flesh, as well as their variety, is of great importance 

 from the sanitary point of view, much stress has been laid upon 

 the methods used for the enumeration of the bacteria. 



This phase of the work necessitated, of course, the use of solid 

 media. As the variety of possible organisms was great it was not 

 advisable to attempt to use a number of special media, but rather 

 to select a few which would be generally available for the great 

 majority of bacteria. Therefore, plain agar neutral to phenolphtha- 

 lein, litmus-lactose-agar, and nutritive glucose gelatin which was 1 

 per cent acid were used in routine work. 



Because of the great variation in the number of organisms develop- 

 ing at different temperatures 6 the plates were incubated at 37, 

 20, and 1.67C. It was found in the progress of this work that 

 the removal of a small amount of tissue with a sterile platinum wire 

 or loop, such as usually suffices for the study of infected flesh, gen- 

 erally gave negative results; and the removal of several such pieces 

 gave results which were not comparable, though every precaution 

 was taken to prevent contamination and to treat each piece exactly 

 as the others were treated. It became necessary, therefore, to 

 remove larger pieces of tissue and to develop some scheme by which 

 these could be disintegrated in a fluid medium which would not 

 affect the organisms and which should have a quantitative value in 

 order that the number of bacteria might be determined for a definite 

 weight of material. Numerous experiments, with varying quantities 

 of tissue and forms of sterile containers, finally evolved the follow- 

 ing technique, which has yielded results that are fairly constant and 

 are comparable. 



Several small pieces of flesh, aggregating from 0.3 to 0.7 of a gram, 

 are removed with sterile instruments from an uncontaminated por- 

 tion of the tissue which is being investigated, and are placed in an 

 Erlenmeyer flask of 25 cc capacity, containing a sufficient number 

 of thin pieces of broken glass to cover the bottom, and which, after 

 sterilization, had been accurately weighed. Reweighing gave, by 

 difference, the weight of the tissue. A measured quantity of a suit- 



a The bacteriological examinations reported have been made by E. Q. St. John. 

 -&Pennington, Bacterial Growth and Chemical Changes in Milk at Low Tempera- 

 tures, J. Biol. Chem., 1908, 4: 353. 



