ANNUAL ADDRESS, MDCCCLXXI. 19 



Nothing could convey a clearer conception of the extreme 

 divisibility and diffusibility of organic matter than the re- 

 cord furnished by that eminent philosopher of his experi- 

 ments and their results. He dealt with particles that 

 would be completely hidden from the highest powers of 

 the microscope, and he was able to prove that such par- 

 ticles were not of inorganic or mineral character, but of 

 organic nature ; that is, they were either complete organisms 

 in themselves or had formed part of living beings of 

 some sort or other. 



The diffusion of such organic matter through every por- 

 tion of the atmosphere struck Dr. Tyndall, as it would 

 any other individual, as offering some explanation of the 

 propagation of disease by infection and contagion. In the 

 invisible cloud of organic particles might well lurk germs 

 of disease, whether particles of diseased matter previously 

 separated or actual germs, living particles endowed with 

 powers of reproduction and capable of setting up diseased 

 action in any favourable soil furnished by animal or plant. 



That epidemic and some other diseases may be pro- 

 pagated by germs was indeed no new theory advanced by 

 Tyndall. It is one of much older date ; but Tyndall's 

 experiments showed us that we need not be astonished 

 at the circumstance that diseased germs have not been 

 demonstrated. They, in fact, proved that such germs may 

 well evade the most penetrating powers of the microscope, 

 and only become cognizant to us in the exercise of their 

 unwelcome operation as inducers of disease. 



The hypothesis of the generation of diseased action by 

 the agency of definite minute organisms has taken wide 

 hold on the medical profession, and several observers have 



