PATHOGENIC MICROBES— INFECTION 125 



this figure a general infection is practically certain ; but on the 

 other hand the same observer states that one bacillus is 

 sufficient to produce fatal anthrax in the mouse. There are 

 certain experimental facts as regards the smallest quantity of 

 bacilli capable of producing tuberculosis but these have not 

 an absolute value. H. Buchner found that to spray looc.c. of 

 a dilution of i per 100,000 of tuberculous sputum was 

 sufficient to give miliary tubercle of the lung to guinea-pigs. 

 The sputum employed contained approximately 80,000 bacilli 

 per c.c. and he calculated that each guinea-pig had been exposed 

 to the attack of 100 bacilli (these figures are of course very 

 approximate). In the experiments of Preisz, xmrtr milligram of 

 sputum, containing about forty bacilli, was found sufficient. 

 In the experiments of Findel, guinea-pigs inhaling about sixty 

 bacilli regularly took tuberculosis.^ 



Microbial Associations. — The microbes which cause 

 diseases are never derived from pure cultures. Their virulence 

 is modified not only by the chemical properties of the 

 medium and the " soil " on which they fall, but by the 

 presence of other species favourable or the reverse. There 

 are streptococci which aggravate diphtheritic sore throats. 

 The coliform bacillus, the torula, and the sarcina described by 

 Metchnikoff favour the production of intestinal cholera. In 

 tetanus the associated bacteria are helped also by other 

 favouring factors, such as splinters, bruising of the tissues, and 

 blood clots. It was formerly thought that the streptococcus of 

 erysipelas was antagonistic to the anthrax bacillus. Pasteur 

 observed an antagonism between the B. pyocyaneus and the 

 anthrax bacillus-; if these two bacteria are inoculated on a 

 medium in lines which cross each other, the anthrax bacillus 

 grows very feebly at the points of intersection. The proteolytic 

 enzyme of the B. pyocyaneus, the pyocyanase, is injurious to 

 many bacteria, and occasionally plays the part of a disinfectant 

 (Emmerich). 



' Tuberculous sputum (caseous material) frequently contains 50,CXX) 

 bacilli per mg. In cultures half-dried on paper there are about 35 to 40 

 millions per mg. — with a possible error of one million (Chausse). 



