DIRECT EXAMINATION 49 



of those micro-organisms which commonly attack foods and 

 drugs, more especially the molds and yeasts. 



c. It is neither practicable nor necessary to dififerentiate 

 between the different kinds of spores which may be present in a 

 product, excepting as suggested under (&). 



i. In many instances it would be desirable to resort to plat- 

 ing methods in order to determine the number of viable organ- 

 isms present. This would be simple for bacteria and mold spores, 

 but more difficult for yeasts. 



Differentiating between Living and Dead Bacteria and other 

 Low Forms of Organisms.— It would be most desirable to deter- 

 mine some practical working method for distinguishing between 

 living and dead bacteria in foods and drugs. Often the question 

 arises as to the time and place source of the contamination. Did 

 the organisms present develop in the fruit, in the pulped material 

 during the processing or in the containers after manufacture? 

 Again, are the organisms estimated by the direct count dead or 

 aUve? 



Several investigators have stated that dead and Hving bacteria 

 react differently with certain stains. For example G. Broca, an 

 Italian bacteriologist, declares that the use of the following mixed 

 stain will serve this purpose. To 8 cc. of concentrated carbol- 

 fuchsin add loo cc. of Loeffler's methylene blue. Let the mixture 

 stand for 24 hr. before using. Exposed to this stain, dead bacteria 

 (killed by heat or by disinfectants) are colored red while Hving 

 bacteria are colored blue. It is declared that other stains, as 

 Giemsa's, will react in a similar manner. 



More recent experiments would indicate that selenium and 

 tellurium compounds will serve to differentiate Uving bacterial 

 contaminations. It would appear that these substances are 

 decomposed into metallic tellurium and selenium when brought 

 in contact with living organisms. Much experimental work 

 along this line has been done by Hansen, Gmelin, Gosio and 

 others, and still more recently (1913) by King and Davis of the 



