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president’s address. 
This portion of the subject has, during the past two or three 
years, deepened and strengthened in interest ; our knowledge of it 
has largely increased ; and the recognition of its vital importance 
has called forth, both in Europe and America, a host of eager and 
- capable workers. It is scarcely too much to say that its wide and 
far-reaching issues are probably the most important to mankind of 
any that have been studied in recent times. Foremost amongst 
the workers in this department may be recalled to you the well- 
known names of Koch and Pasteur, abroad ; and of Lister, Watson- 
Cheyne, and Crookshank, in this country. But the names of other 
eminent investigators will almost necessarily occur to your minds. 
It has long been known what potent factors were microscopic 
Germs in producing changes in the constitution of decaying matter ; 
and how they were, in all probability, the useful scavengers of 
nature, definitely resolving into their constituent elements failing 
and dying organic tissues. But it has become more and more 
a matter of knowledge, that by their parasitic habits and their 
power of invading and living upon and within other living tissues, 
they are also the sources of many so-called diseases of both 
vegetables and animals. 
With regard to vegetable parasitic growth I will not now detain 
you. The blights, and the mildews, and the ergots, as well as 
minuter forms, such as algae and micrococci, are well known ; and 
no doubt much more is still to be learned from their further 
investigation ; whilst by analogy it seems highly probable that the 
circulating fluids of higher members of the vegetable kingdom 
may be found to be invaded by parasitic beings in the same way 
as their animal compeers. 
But it is to Germ life in animal bodies that I wish now specially 
to allude. I have said that our knowledge in this direction has, 
even in the last two or three years, made enormous strides, and 
it is now almost a matter of certainty that all contagious or 
infectious disorders, as well as many others, are but the expression 
of the fact that minute living bodies have made a resting-place for 
themselves in or upon other living tissues ; and that the develop- 
ment of the phenomena of these morbid states is but an indication 
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