600 MICROBIOLOGY OF FOODS 



this hypothesis. There can be no doubt that the bacteria do enter 

 intimately into intestinal digestion and in some instances bring ,bout 

 changes beneficial to their host, such as the digestion of cellulose, 

 whereas when furnished other food they may exert a harmful influence, 

 as for example in excessive intestinal putrefaction. 



In diseased conditions of the gastro-intestinal tract one finds more 

 or less well-marked alterations in the faecal flora. These changes 

 include quantitative change in the total bacterial output, change in 

 the proportional relationships of the various normal types and finally 

 the appearance of new or foreign types of organisms, either harmless or 

 pathogenic. In many instances there is furthermore a distinct tendency 

 for some members of the normal intestinal flora to assume pathogenic 

 properties and invade tissues rendered less resistant by disease. 



Among the intestinal microorganisms which may assume patho- 

 genic r6les at. times may be mentioned B. coli, B. vulgaris, Ps. pyo- 

 cyanea, B. bifidus, Bad. Welchii, the streptococci, micrococci and 

 Trichomonas intestinalis. Among the definitely pathogenic forms are 

 B. typhosus, Msp. comma (Sp. cholera asiatica), B. paratyphosus, B. 

 enteritidis, Bact. dysenteric, Bact. anthracis, Bact. pestis, Bact. tuber- 

 culosis, Entamceba dysenteric (histolytica) , Coccidium hominis and 

 Lamblia intestinalis. 



The technical procedures necessary for the recognition of some 

 of these organisms in the fasces and for their isolation in pure culture 

 are in some instances highly specific. Thus if one is searching for 

 B. bifidus it is best to employ dilution cultures in tall tubes of glucose 

 agar inoculated with faeces of a healthy nursling. The same material 

 plated on gelatin will yield only colonieslcf B. coli. Bact. Welchii is most 

 readily isolated by pasteurizing a suspension of the faeces and introduc- 

 ing it into blood broth or litmus milk in a Smith fermentation tube. 

 The cholera organism is searched for by introducing considerable 

 quantities of faeces into flasks of pepton-salt solution and transplanting 

 from the surface film after six hours to new flasks. On account of 

 its very rapid multiplication in this medium the cholera germ, if 

 present, outstrips the other faecal bacteria. Subsequently it is necessary 

 to apply specific agglutination tests to the spirals thus obtained in order 

 to recognize them with certainty. The typhoid bacillus, on the other 

 hand, is sought by inoculating media containing substances which 

 restrain bacterial growth in general without inhibiting the growth of 



