oct.8, igji Microscopic Study of Bacteria in Cheese 97 



isms together with their morphological and other general characteristics, 

 but an attempt to enumerate these types involves other difificulties. 



The direct examination of cheese in the different ripening stages is 

 advantageous and important, since the different groups of organisms 

 can be studied as they actually occur in the cheese mass, and their 

 groupings and relative relationships noted. The grouping may be 

 especially important when considered in relation to the number present. 

 For example, an organism may be present in large numbers during the 

 early stages of ripening, but appear in scattered and isolated groups 

 containing only a few individuals. In some instances only single bac- 

 teria were found through the mass. In such cases the total number of 

 this group by the plate count may be large, but the grouping, as deter- 

 mined by direct examination, may demonstrate that they are not ac- 

 tively growing and playing a part in the ripening of the cheese. On 

 the other hand, the presence of large clumps of organisms, with the size 

 of the clumps increasing during ripening, indicates that such groups are 

 developing in the cheese mass and are probably playing an important 

 r61e in the changes involved. 



That this grouping of the organisms actually occurs can be seen in 

 Plate 17, A. In this photomicrograph are shown the types and groupings 

 of organisms found in a very green cheese, showing that the Streptococcus 

 lactis-like organisms predominated and were scattered in pairs over the 

 field. Any migration of these bacteria through the cheese mass appears 

 to have been impossible, and one is impressed with the fact that growth 

 and reproduction could not have been taking place rapidly or the number 

 of individuals per group would have been larger. In Plate 17, B, which 

 represents a section from a cheese 5 months older than that shown in 

 Plate 17, A, the organisms are found in larger clumps with many of them 

 so massed that accurate counting is impossible. From the examination 

 of a series of sections from cheeses of varying ages, it has been found that 

 the clumps increase in size as the cheese ripens, reaching a limit after 

 seven to eight months. It is evident that the organisms in the clumps, 

 mostly cocci and a few rods, are thriving and reproducing and must, 

 therefore, change the surrounding medium as they utilize it for food. 

 It is not within the scope of this paper to discuss the significance of this 

 occurrence but only to point out that such variations are found when 

 samples are examined directly. 



QUANTITATIVE EXAMINATION 



An objection often made to counting organisms in microscopic prepa- 

 rations of dried liquids is the uneven thickness of the resultant dried 

 film. This objection is eliminated when parafiin sections are used, as 

 such sections are uniform in thickness and the organisms remain in their 

 natural relationships. Boekhout and DeVries (z) at one time endeavored 



