602 



MICROBIOLOGY OF FOODS 



A preliminary classification of the recognizably different kinds of microbes 

 should be made by microscopic examination of film preparations stained (i) with 

 LoefHer's methylene blue, (2) by Gram's method, (3) by the Ziehl-Neelsen method 

 and (4) simply withLugol's solution. It is best to count from 500 to 1,000 microbic 

 cells as they are met with in successive microscopic fields and to classify them 

 according to form, size and structural details brought 

 out by the different stains. Permanent records and, if 

 possible, permanent mounted preparations should be 

 preserved, so that the microbes subsequently brought 

 to development in the cultures may be identified with 

 some of those present in the microscopic picture of 

 the original material. 



Cultures are best made upon a quantitative basis, 

 employing for inoculation measured amounts of accur- 

 ately prepared dilutions of the original material. There 

 is no single culture medium or method which can be 

 relied upon to give any approximate conception of the 

 numerical relations of the microbes of the digestive tract. 

 Each cultural method necessarily favors certain species 

 present in the mixture and allows others to develop 

 only poorly or not at all. Adequate information con- 

 cerning the quantitative relationships is obtained only 

 by comparing the results of the culture work with the 

 direct quantitative estimations and by fitting the cul- 

 tural results into the original microscopic picture. A 

 great variety of culture media and culture methods, 

 aerobic, anaerobic and micro-aerophilic, must be em- 

 ployed in making even an incomplete general survey of 

 the microbes from any portion of the digestive tract. 

 For the detection of certain single species, on the other 

 hand, one may sometimes rely upon a single medium, 

 such as blood-agar for the streptococci of the mouth, 

 LoefHer's serum for diphtheria bacilli in the pharynx 01 blood-broth in fermenta- 

 tion tube for spores of B. welchii in the faeces. Thus the numerous time-consuming 

 procedures may be very much abridged and many of them may well be omitted 

 when one wishes to ascertain merely the presence or absence of a certain single 

 species of microbe. 



GENERAL REFERENCES ' 



Schmidt und Strasburger, Die Faeces des Menschen, IV " Auflage, Berlin, 1914. 



Kuester, Die Flora der normalen Mundhohle, Kolle und Wassermann, Hand- 

 buch, IP Auflage, Jena, 1913, VI, 435-449. 



Kuester, Die Bedeutung der normalen Darmbakterien fur den gesunden Men- 

 schen, Kolle und Wassermann, Handbuch, II" Auflage, Jena, 1913, VI, 468-482. 



FIG. 155. Two types 

 of instrument for obtain- 

 ing faeces from infants for 

 bacteriological examina- 

 tion. (After Schmidt and 

 Strasburger.) 



