xxvi President's Address 



decay of animal and vegetable matter is entirely due to 

 parasitic organisms which assert their dominion the instant 

 the vital forces in either cease, or even fall below a certain 

 standard; there is no decay without these, and Professor 

 Tyndall shows how they can be kept from their prey. 

 Under the ordinary circumstances of life these organisms 

 doubtless play a beneficial part in the great scheme of 

 nature, but the subtle and invisible power which has thus 

 been revealed to us is also capable, under certain conditions, 

 of acting most deleteriously upon human health and life, 

 and there is a steadily-gi'owing conviction that they play a 

 most important, if not the only part, in many contagious as 

 well as simply septic diseases. Should this be demonstrated 

 beyond a doubt, which I think far from improbable, the results 

 arrived at by Professor Tyndall unmistakably indicate the 

 direction which any effort at prevention of such diseases 

 must take ; and it becomes manifest that no researches in 

 etiology can claim to be scientific or aiming at the truth 

 which ignore the grand work that has been, and is being, 

 done in this branch of biological science. One of the most 

 remarkable achievements in physical science efiected daring 

 the present year is the liquefaction of oxygen, nitrogen, and 

 hydrogen gases, and the solidifaction of the last named — 

 results approached by the experiments of M. CaUetet, in 

 Paris, and about the same time realised in a far more pro- 

 nounced form by M. Raoul Pictet, at Geneva. Our expe- 

 rience of the three states of matter — the solid, liquid, and 

 gaseous forms, and of the facility with which water, for 

 example, passes from solid ice to the fluid state, and from 

 the latter to the state of vapour — has long since led to the 

 hypothesis which assumes that all material substances which 

 are not decomposed by alteration of temperature are capable, 

 under suitable influencing circumstances, of passing through 

 these three phases ; and very much effort has been devoted 



