xxi] PATHOGENIC ORGANISMS 549 



fails to cause disease, it becoming soon killed herein. If then 

 we are to judge of the nature of a microbe by its behaviour 

 in the peritoneal caviiy of the guinea-gig, i.e. whether patho- 

 genic or non-pathogenic, we should have to include among 

 the pathogenic class a large number of microbes which are 

 generally pure saprophytes, while we should have to exclude 

 from that class microbes which, as a matter of fact, are 

 notoriously specific. If, on the other hand, we distinguish 

 the microbes by the presence or absence of poisonous 

 substances in their bodies (intracellular poisons or proteins) 

 or elaborated (or secreted) by them while growing and multi- 

 plying — toxins — we do not get much further either ; because, 

 as I have shown and as has been mentioned in a former 

 chapter, some notoriously specific microbes have not these 

 intracellular poisons (anthrax, fowl cholera, diphtheria), 

 while other notoriously saprophytic bacteria possess them 

 (vibrio of Finkler, bacillus prodigiosus, bacillus coli, &c.). 

 Again, if we judge by this whether a microbe does or does 

 not produce in the course of its growth and multiplication 

 toxins, i.e. poisonous metabolic substances, we would not 

 get at a true definition either, because some microbes con- 

 nected with putrefactive changes (proteus vulgaris) produce 

 well-specialised toxic principles, while other microbes, 

 connected with infectious diseases, do not, as far as one can 

 judge from experiments, produce any speciahsed toxin, e.g. 

 the whole group of microbes which cause in the rodent 

 haemorrhagic septicaemia ; then there are other microbes, true 

 specific or pathogenic, which although producing highly 

 specialised toxin, i.e. toxin which injected into the animal 

 causes the same disease as when we inject the living 

 microbe (tetanus, diphtheria), do not as a rule live' in the 

 blood or in the tissues : the bacillus diphtheria, the bacillus 

 tetani, lives chiefly at the seat of inoculation, where it produces 



