BACTERIAL DISEASES OF THE ANIMAL KINGDOM 119 



1 -5-2 /J, in length and about 0-4 /x in breadth. The " commas " some- 

 times become attached and thus form a combination, something similar 

 to the letter S in shape. This organism is found, during the disease, 

 only in the intestines : it does not enter into the blood or attack an)' 

 of the other internal organs. It also thrives as a saprophyte in various 

 kinds of decomposing matters, though 

 very little is known of its saprophytic 

 habit. The conditions promoting its 

 growth are a fairly high temperature, 

 a plentiful supply of oxygen and of 

 organic material. This microbe is easily 

 killed, being very susceptible to drying. 

 Hence we do not find that cholera 

 epidemics spread very far from their 



starting points, unless the microbe is f.g. 73. -Cholera spkiiiun,. 



carried by ships or by other means of 

 transit. The spread of this disease is almost always due to the access 

 of choleraic discharges to the water supply. As flies fed on material 

 containing the cholera microbe can retain the latter in a live con- 

 dition for twenty-four hours, it is probable that insects are also 

 instrumental in serving as vehicles for the transmission of this disease. 



Very little is known of the poison secreted by the cholera microbe. 

 It has been separated, but only in an impure condition. When animals 

 are inoculated with it all the symptoms of cholera rapidly appear, even 

 though the organism itself which produced the poison has been killed. 

 Since Koch's researches (published in 1884) the cholera germ has been 

 extensively studied, and as the cause of the disease is known, the 

 methods of combating this scourge have attained a high degree of 

 eflBciency. 



Another dreaded parasite is Eacillus tuberculosis, which also confines 

 its growth to limited areas. This microbe is widely distributed, and 

 is responsible for consumption, " white swelling ' of joints, lupus, 

 scrofula, etc. It may attack almost any organ in the body ; thus it 

 may be found only in a small spot in the lungs, or in one joint or in 

 one gland ; but, on the other hand, invasion may take place from these 

 spots and several organs become infected. This invasion may be slow 

 or rapid, and if persistent will end fatally. The discovery of this 

 germ is due to Koch, whose research on this subject is one of the 

 masterpieces of bacteriological science, on account of the enormous 

 difiiculties which he successfully overcame. Bac. tuberculosis attacks 

 domestic animals with deadlier effect than any other microbe. It is 



