Vice-President’s Address. ) 
popular mind that they are readily recognised as being the 
potential causes of numerous diseases. 
Let us for a few moments turn our attention to the history 
of these minute organisms. We are at once struck by the 
fact that even the earliest observers appear to have looked 
for the causation of disease in minute organic and organised 
beings, as they were convinced that the symptoms of disease 
could be produced only as the result of the action of living 
protoplasm ; and we find in Kircher’s “ Pathologia Animata ” 
the first attempt to evolve a parasitic theory of disease, which, 
imperfect as it was, foreshadowed the better-founded and 
more accurate theories which within the last thirty years have 
been so well put forward and so ably supported. The first 
authentic description of these organisms, however, was given, 
not in connection with disease processes, but with some of 
the common processes of everyday life. Leeuwenhoek in 
1675, or four years after Kircher’s book had been published, 
discovered in an infusion of pepper, in the intestinal canal 
of horses, flies, frogs, pigeons, fowls, and even in his own 
diarrhcea stools, small moving and living forms of such 
extreme minuteness that hitherto their very existence had 
escaped the notice of the most careful observers with the 
somewhat primitive lenses they then had at command. Eight 
years later this same observer described minute organisms in 
the material taken from the teeth, that we now recognise, 
from his descriptions and drawings, as bacteria. Of them he 
says:—‘“On reflecting on these substances, I thought it 
probable (though I could not observe any motion in it) that 
it might contain small living creatures, Having therefore 
mixed it with rain-water which I knew was perfectly pure, 
I found to my great surprise that it contained many small 
animalcules, the motions of which were very pleasant to 
behold. The largest sort of them is represented in plate v., 
fig. 3, at A‘ (evidently a somewhat spindle-shaped bacterial 
form or clostridium), and these had the greatest and the 
quickest motion, leaping about in the fluid like the fish 
called the jack: the number of these was very small. The 
second sort are represented at B (a shorter, plumper organism), 
1 Leeuwenhoek’s Works, translated by Samuel Hoole, London, 1800, 
