598 MICROBIOLOGY OF FOODS 



kinds of microbes in the faeces varies considerably even in health, depend- 

 ing upon various factors, among which age of the individual and 

 character of the food are very important. 



The first meconium passed after birth may contain few or no micro- 

 organisms. Within a few hours, however, they appear in the intestinal 

 discharges. The earliest forms are usually large diplococci to which 

 are soon added various bacilli, small diplococci and tetrads. Among 

 the bacilli, a long slender form with a large oval terminal spore, the 

 headlet bacillus of Escherich, is particularly conspicuous. B. coli is 

 also present at this time and several gelatin-liquefying forms of bacilli 

 can be isolated in cultures, among them B. (Proteus) vulgaris and B, 

 subtilis. Anaerobic cultures demonstrate the presence of Bact. Welchii, 

 B. edematis and B. bifidus. 



As the meconium is replaced by the residue of the ingested mother's 

 milk, the previously variegated bacterial flora suddenly becomes very 

 simple and during the whole period of exclusively breast feeding the 

 stools contain enormous numbers of the Gram-positive micro-aerophilic 

 B. bifidus of Tissier, with only small numbers of B. coli and very few cocci. 

 The dominance of B. bifidus may readily be demonstrated by making a 

 series of dilution cultures in tall tubes of glucose agar, according to the 

 method of Veillon, and incubating them for five days or more. When 

 the child begins to take cow's milk there is a sudden increase in the 

 relative numbers of B. coli and streptococci and with the addition of 

 starchy foods to the diet the faecal flora gradually comes to resemble 

 that of the adult. 



In the heal thy adult taking a mixed diet, the faecal flora consists for 

 the most part of Gram-negative bacilli of the type of B. coli. There are 

 also many diplococci, a few small Gram-positive bacilli (B. bifidus?) a 

 small number of Bact. Welchii and its free spores, a few representatives 

 of the B. edematis group and a variable number of slender spirochetes. 

 Aerobic plate cultures on agar or gelatin often bring to development 

 only B. coli. When a vegetarian diet rich in indigestible residue is 

 consumed, the diplococci are much diminished in numbers; numerous 

 large bacilli, Bact. Welchii and B. subtilis, take their place. The con- 

 sumption of excessive quantities of meat and starchy foods may lead 

 to a considerable increase in the numbers of the Bact. Welchii group and 

 some of the bacteria of this group may be stained brown or blue with 

 iodine because of the granulose which they contain. The bacteria 



