40 MICROBES AND TOXINS 



or the same appetites ; one requires more alkalinity, another 

 requires a certain degree of acidity. The unused residue of the 

 food of one may provide excellent nourishment for another. 

 Their actions on elementary waste products have to follow each 

 other in a regular and chemically definite order. Hence we get 

 agreements and antagonisms, one species, by reason of its 

 nature and the food of its host, being towards another either 

 a help or a hindrance. 



This idea was first expressed in connection with the bacteria 

 of the intestine by the experiments of Metchnikoff on cholera 

 and its vibrio. Cholera is due to the multiplication in the 

 intestine of a spirillum, which rarely penetrates into the blood, 

 but elaborates in the intestine poisons which diffuse and kill 

 the patient. Cholera is an acute, toxic, specific enteritis. 

 Koch's discovery of the spirillum or " comma bacillus " of 

 cholera had to contend with an obstinate scepticism, because 

 cholera could not be produced with it at will in laboratory 

 animals, unlike anthrax or fowl-cholera. Whether by inoculation 

 under the skin, or in the peritoneum, or by the mouth, the 

 result was the same. Even when several savants swallowed 

 cultures of it, the results of these experiments "in anima nobili" 

 were very inconstant. In this, typhoid fever resembles cholera, 

 the disease being very difficult to reproduce experimentally; 

 it is only quite recently that experimental typhoid fever has 

 been successfully produced by employing the higher apes, the 

 nearest congeners of man. 



It cannot be a matter of indifference to the cholera vibrio 

 what is the nature of the flora of the alimentary canal into 

 which it penetrates. By a very simple method of experiment, 

 namely, by inoculating together on gelatine plates vibrios and 

 various other microbes along lines which crossed each other, 

 Metchnikoff was able to prove that the association of certain 

 bacteria favoured the growth of cholera while others inhibited 

 it. Round the colonies of a favouring bacterium a swarm 

 of little cholera colonies developed. Various favouring and 

 inhibiting bacteria were discovered in the air, among animals, 

 and most interesting of all in the human stomach. 



