XXI] PATHOGENIC ORGANISMS 551 



much smaller dose injected subcutaneously causes tumour 

 and fatal issue in thirty to thirty-six hours. But also in the 

 subcutaneous tissue of the guinea-pig the above saprophytes 

 can live and multiply, provided they are injected in large 

 doses ; a swelling appears, which is as a rule only of a 

 temporary nature, lasting for from a few days to a week, 

 according to the dose, and sometimes leading to abscess or 

 purulent infiltration and necrosis. While the tumour lasts 

 the microbe injected can be demonstrated in a living state 

 by the culture test. In very large doses they may even 

 produce rapidly general infection and death. On the other 

 hand we see that even in the case of well-recognised specific 

 microbes the subcutaneous injection may produce no 

 appreciable result or only a slight and transitory tumour 

 and recovery. 



We have mentioned in several instances such results 

 having been obtained by using attenuated cultures ; it is 

 this result which represents the essence of protective inocu- 

 lations. A temporary tumour can be therefore produced 

 by a specific microbe of attenuated virulence or by an 

 otherwise virulent microbe if it be injected in too small a 

 dose, or into an animal which is not very susceptible ; ac- 

 cording to. any or all of these factors the effect of inoculation 

 may be nil, or very slight and rapidly passing, or it may be 

 moderate and slowly passing off, or it may be conspicuous and 

 leading to death. So that the microbe introduced, although 

 specific and pathogenic, may degenerate and be killed 

 rapidly in the tissue, or it may multiply slightly, or it may 

 multiply rapidly and easily and cause general infection. 



From these considerations it follows then both in the 

 case of true saprophytic as of true pathogenic microbes that 

 all gradations of their capability to live and thrive in the 

 animal tissues may be shown to be demonstrable, these 



