EXPERIMENTAL INOCULATION 467 



can state generally that the conditions favourable for the growth 

 of the cholera spirillum are a warm temperature, moisture, a 

 good supply of oxygen, and a considerable proportion of organic 

 material, we do not know the exact circumstances under which 

 it can flourish for an indefinite period of time as a saprophyte. 

 The fact that the area in which cholera is an endemic disease is 

 so restricted, tends to show that the conditions for a prolonged 

 growth of the spirillum outside the body are not usually supplied. 

 During recent epidemics the cholera organism has been culti- 

 vated from the stools of a considerable number of people 

 suffering from slight intestinal disturbance, and even from the 

 stools of quite healthy individuals ; these, may be regarded as 

 " cholera-carriers." Numerous observations, carried out both on 

 convalescents and on contacts having the spirillum in the stools, 

 show that in the great majority of cases it dies out after two 

 or three weeks and usually earlier ; it has, however, been found 

 as long as twelve months afterwards. Greig has found that 

 the excretion of the organism in the stools of carriers is of an 

 intermittent character ; accordingly several examinations are 

 necessary before they can be pronounced free. There is no 

 doubt that carriers play an important part in the spread of the 

 disease, and can originate epidemics. 



Cholera organisms are, as a rule, rapidly killed by being 

 thoroughly dried, and it is inferred from this that they cannot 

 be carried in the living condition for any great distance through 

 the air, a conclusion which is well supported by observations 

 on the spread of the disease. Cholera is practically always 

 transmitted by means of water or food contaminated by the 

 organism, and there is no doubt that contamination of the 

 water supply by choleraic discharges is the chief means by which 

 areas of population are rapidly infected. It has been shown 

 that if flies are fed on material containing cholera organisms, 

 the organisms may be found alive within their bodies twenty- 

 four hours afterwards. And further, Haffkine found that 

 sterilised milk might become contaminated with cholera organ- 

 isms if kept in open jars to which flies had free access, in a 

 locality infected by cholera. It is quite possible that infection 

 may be carried by this agency in some cases. 



Experimental Inoculation. — In considering the effects of 

 inoculation with the cholera organism, we are met with the 

 difficulty that none of the lower animals, so far as is known, 

 suffer from the disease under natural conditions. Accordingly, 

 attempts to induce the multiplication of the organism within 

 the intestine of animals by artificially arranging favouring 



