MICROSCOPIC STUDY OF BACTERIA IN CHEESE 



By G. J. HucKBR 



Associate in Research, New York Agricultural Experiment Station 



INTRODUCTION 



Heretofore cultural methods have ordinarily been used in the study 

 of cheese flora, but the usual routine technic has given only an inade- 

 quate conception of the number and types of bacteria present. Although 

 these cultural methods were employed in order to secure an idea of the 

 number and varieties of organisms occurring in cheese, they have failed 

 to establish the relative abundance of each type of microorganism in 

 the cheese. This objection remains valid in the light of both quantita- 

 tive and qualitative studies. 



The so-called "dilution technic," which involves the mass action of 

 the organisms, has proved valuable in determining the type or group of 

 organisms which predominates in a given sample ; but it does not furnish 

 information regarding the general flora. This method often tends to 

 give erroneous results, especially when the dilution medium used favors 

 the growth of special groups. Under such conditions the results are 

 influenced by the selective action of the medium. This has been true 

 where milk was used as a dilution medium in examining cheese. The 

 milk favored the growth of the lactic acid group; while the inert and 

 nonlactose fermenting types or slow-growing cocci were overgrown, due 

 in a large measure to the selective action of the medium. This procedure 

 has well served its purpose in assisting to isolate the organisms for 

 which it has a special adaptation. 



In general, cultural methods are preferable to a microscopic examina- 

 tion because cultures can be isolated and studied independently — a 

 feature which will always remain the outstanding advantage of these 

 methods. 



Although subject to the same limitations as any microscopic method, 

 the following method has been successfully used in this laboratory and 

 has been employed in a routine way in determining the number of bac- 

 teria in cheese. 



HISTORY 



Johan-Olsen {Sy, working with the molds which ripen "Gammelost" 

 (a Norwegian cheese), mentions a sectioning method and implies that 

 it resembles the usual histological technic but does not outline the 

 procedure in detail. 



' Reference is made by number (italic) to "Literature cited," p loo. 



Journal of Agricultural Research, Vol. XXII, No. i 



Washington, D. C Oct. 8, 1921 



(93) 

 54818°— 21 4 



Key No. N. Y. (Geneva) ,-6 



