70 BACTERIOLOGY 



on excrement from cholera cases, and human " carriers," either 

 contacts or convalescents, are also centres of infection. 



In the cholera patient, the presence of the organism is re- 

 stricted to the intestinal canal, especially the small intestine, 

 from which the absorption of toxins takes place. Extensive 

 damage is produced in the mucous membrane of the bowel, 

 with congestion, necrosis, and ulceration, the contents being 

 fluid, stinking, and blood-stained, with shreds of mucus, lymph, 

 and cells, constituting the " rice-water " stools so character- 

 istic of the disease. The organism swarms in these, often in 

 enormous numbers. 



Microscopically, it is a small curved organism or vibrio, often 

 called, after its discoverer, Koch's Comma Bacillus (see Frontis- 

 piece, fig. 13). It is very actively motile, and possesses a long, 

 delicate, vibratile flagellum at one end (see Fig. 9, a). It may 

 sometimes form spiral chains, and involution or degeneration 

 forms are common. It is Gram-negative. 



It is easily cultivated, growing readily and rapidly on ordi- 

 nary media, especially if incubated at body-temperature with 

 an abundant supply of oxygen. It forms a scum on the surface 

 of liquid media, and liquefies gelatin, producing in a stab 

 culture a characteristic bubble or bell-shaped area of lique- 

 faction, which later becomes more funnel-shaped. In peptone- 

 water or peptone-broth it produces indole and nitrite from 

 the splitting of the protein a red reaction, called " Cholera- 

 Red," being obtained with suitable chemical tests. 



In culture and in ordinary water it may remain alive for 

 long periods, but is easily killed by antiseptics and by heat and 

 drying. It is important to remember its tendency to grow at 

 the surface near the air, as, in examining a water-supply, the 

 specimen is best taken from the surface. For the diagnosis of 

 the disease, in addition to the finding of the vibrio in the in- 

 testinal discharges and its characters on culture, the aggluti- 

 nation test (see p. 49) and bacteriolytic (Pfeiffer's) reaction 

 (see p. 49) are of great importance. Serum-treatment has 

 not yet met with much success, but prophylactic as well as 

 therapeutic vaccination are now widely practised. 



Many other vibrios, mostly non -pathogenic, though some 

 may cause disease in animals, are found, especially in the water 

 of certain rivers. 



Coli-Typhoid Group. This is a very important and highly 

 complex group, which contains many actively pathogenic and 

 some comparatively harmless members. Many of them are 

 more or less intermediate between saprophytes living on dead 

 organic matter, and parasites living on or in living tissues, 



