550 MICRO-ORGANISMS AND DISEASE [chap. 



its toxin ; in the blood or tissues it as a rule does not seem 

 capable of existing. Further : there are microbes which are 

 capable of producing specialised toxins when growing in one 

 kind of medium but not in another ; bacillus anthracis is a 

 good case in point : it would be extremely difficult — in fact 

 it has not succeeded hitherto — to obtain from a broth 

 peptone culture of bacillus anthracis, however luxuriant, any- 

 thing like the specific toxin that was obtained by Wooldridge 

 in cultivations in fluid alkali albumen, by Hankin in fibrin, 

 by Sidney Martin in albuminous fluid. Or take the cholera 

 vibrio. This microbe does not produce toxic substances to 

 any appreciable degree in broth culture, but in albuminous 

 fluids (van Ermengem) it produces it in a concentrated form. 

 I have found the same to be the case with the vibrio of 

 Finkler, bacillus coli, and others. From all this it follows 

 that the presence or absence in the microbic bodies of 

 principles poisonous to the animal body or of poisonous 

 principles produced in culture is no guide in distinguishing 

 a pathogenic from non-pathogenic microbes. Equally un- 

 satisfactory is the distinction into microbes which can and 

 such as cannot grow and thrive in the tissues of an animal, 

 the former being generally considered pathogenic, the latter 

 non-pathogenic. We have already mentioned the fact that 

 some notorious saprophytes not connected with any specific 

 disease — e.g. bacillus prodigiosus, bacillus coli, proteus 

 vulgaris, vibrio Finkler-Prior, bacillus subtilis, and others — 

 can live and multiply in the peritoneal cavity of a guinea- 

 pig, provided they are injected therein in comparatively 

 large quantities, whereas a notorious specific or virulent 

 microbe, e.g. the bacillus diphtheriae taken from a gelatine 

 culture, cannot live in the peritoneal cavity even if intro- 

 duced in large quantities; it rapidly in the course of a few 

 hours degenerates and dies, whereas of the same culture a 



