392 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



plished by placing fecal material in a flask of broth kept 

 at blood heat. The organisms of various types multiply, 

 but, the cholera and other vibrios are most abundant near 

 the surface of the medium, that is, they are attracted to the 

 higher concentration of oxygen. A loop full of the surface 

 film examined microscopically will usually show vibrios if 

 they are present. The organism may then be isolated by use 

 of an alkaline egg medium which will inhibit the growth of 

 other types of bacteria. The organism is easily destroyed 

 by heat. It produces acid from dextrose but no gas. Indol 

 is formed. The Vibrio cholerce liquefies gelatin. Milk is not 

 coagulated. 



Pathogenesis. The cholera vibrio is not markedly 

 pathogenic for laboratory animals. The disease in man is 

 acquired in much the same manner as is typhoid fever. The 

 bacteria are excreted in the stools and the disease is trans- 

 mitted only by ingestion of such material in water, milk or 

 food. 



The disease may be characterized as an extremely acute 

 type of diarrhea. The organisms multiply in the alimen- 

 tary tract, producing a poison which causes more or less 

 desquamation of the lining membrane of the intestines. 

 This appears in the watery stools as white particles, some- 

 what resembling grains of rice, whence the name rice-water 

 stools. The disease is usually fatal. 



Vaccination against the disease by the use of cultures 

 killed by heat or considerably attenuated has been success- 

 fully practiced. 



