ORGANISMS WHICH PRODUCE DISEASE 71 



ready to take on a pathogenic character. All are more or 

 less similar in their morphology. If well grown they are 

 usually short, plump, straight, Gram-negative bacilli with 

 rounded ends, some being motile, others not. None of them 

 liquefies gelatin, and none forms spores. Most of them grow 

 easily on all the ordinary media, and differ widely in their 

 power of fermenting various sugars and other substances, 

 a property made use of in differentiating them one from another. 

 Each is agglutinated in high dilution by its homologous serum, 

 i.e. the serum of an animal or patient infected with the specific 

 organism to be tested a fact which constitutes one of the 

 most delicate means of differentiating them one from another. 

 The name Typhaceae has been applied by Loffler to the 

 whole Coli-Typhoid group, and they may be divided roughly 

 into three chief sub-groups : 



1. The Coleae, including B. coli and its relatives and certain 

 closely allied Capsulated Bacilli. 



2. The losarceae or Meat-Poisoning Group. 



3. TheTypheae^ncludingjB.fypAoswSjthedysenterybacillijetc. 

 Enormous numbers of differential tests, especially the effects 



of their fermentation activities upon various special culture- 

 media, have been introduced for isolating and determining 

 the identity of these organisms. Speaking generally, the first 

 of these sub-groups contains members which are very active 

 fermenting agents, the third are much less active, whilst the 

 second group is intermediate in its activity ; but for details, 

 reference must be made to larger works on bacteriology, com- 

 plicated tables of these reactions having been drawn up for 

 workers specially interested in this great group of organisms. 

 Only a few more important members need be mentioned here. 



Coleae : Bacillus coli is one of the most widely diffused 

 organisms in nature. It is found in enormous numbers in the 

 intestine of man and most other animals, and it is therefore 

 found in water, soil, dust, or wherever faecal contamination, of 

 which it may be taken as an index, is to be found. In its usual 

 form in the intestine it may be regarded as a harmless organism 

 combining the roles of saprophyte and semi-parasite, and 

 indeed, aiding in the breaking up of food in the large intestine, 

 in which, especially in the caecum, bacterial digestion is now 

 recognised as playing an important part in the animal economy. 

 There are, of course, many other varieties of organisms also 

 present in the bowel Streptococci, Staphylococci, Coliform 

 Bacilli, and numerous other aerobic and anaerobic bacteria, 

 which also take part in this process, and which may, along with 

 other organisms not normally inhabitants of the bowel, under 



