THE PRESIDENT'S ADDRESS. 271 



increases in amount until there is enough to produce its deadly 

 effects, when the characteristic symptoms of disease manifest 

 themselves in the patient. 



Buckmaster considers that most of the filterable parasites are 

 Bacteria, but as we know nothing of their structure it seems a 

 little premature to include them in any group which is based upon 

 morphological characters. They might be included in Weismann's 

 hypothetical Biophoridae, although, from the point of view of the 

 higher organisms, ; ' death -carriers" would certainly be a more 

 appropriate name for them than " life-carriers." 



Inasmuch as all the known filter-passing organisms are 

 parasitic, it might be argued that their existence implies the 

 pre-existence of higher organisms, and that therefore they cannot 

 be regarded as themselves representing the most primitive living 

 things. Such an argument would, of course, be entirely 

 fallacious. It so happens that at the present time the only 

 means we have of recognising the most minute of these 

 organisms is by their effects upon other organisms. There may 

 be hosts of ultra-microscopic organisms living freely on the earth's 

 surface which have no recognisable effects upon the higher plants 

 and animals, and of whose existence we therefore remain in 

 complete ignorance. This would be quite in harmony with what 

 we know of the microscopically visible Bacteria. Some of these 

 live freely in the soil and are able to feed upon purely inorganic 

 substances, while others are far more familiar to us on account 

 of their influence, whether beneficial or disastrous, either upon 

 ourselves or upon other organisms in which we happen to be 

 interested. 



Your late President, Prof. E. A. Minchin, who speaks with 

 great authority on such subjects, in his last address to the Club, 

 devoted some time to the consideration of the question whether 

 the extremely minute organisms which we have be?n discussing 

 consist of cytoplasm or chromatin, and pronounced in favour 

 of the latter alternative. For my own part I must confess that 

 I prefer the view that at this stage of evolution the distinction 

 between cytoplasm and chromatin has not yet arisen, a view 

 which, as Prof. Minchin pointed out, is in harmony Avith the 

 hypothesis of the evolution of living matter from inorganic sub- 

 stances on the earth rather than with that of its importation 

 from some other planet. 



