159 
Mr. Brooke, V.P. — I have been very much gratified by this paper of 
Professor Kirk’s, and although I have not heard the whole of it here to-night, 
I may say that I carefully read it all before I entered this room. I must 
fully endorse the conclusions at which Mr. Kirk has so ably arrived ; but it 
occurred to me while the latter part of the paper was being read, to offer just 
one illustration which may not be unacceptable, of the fact that the non- 
visibility of matter in a fluid is no proof whatever of its non-existence. 
Many years ago the late Professor Faraday gave me a bottle containing a 
clear, transparent fluid of a reddish-purple* tint. Now that fluid was known 
to contain gold — it was water, in fact, in which gold was suspended in an 
extremely minutely subdivided form, and Professor Faraday gave me the 
bottle in order that I might subject it to a careful microscopic examination, 
to see if the highest power of the microscope could detect material particles 
of gold in it. The little gold particles were so evenly distributed that they 
remained suspended in the fluid and did not subside, but they simply commu- 
nicated to the water that purple tint which gold possesses when viewed in 
transmitted light. If you take a piece of gold leaf between two plates of 
glass and look through it, you wall find that it freely transmits light of a 
purple colour. I submitted the fluid to the very highest powers which the 
microscope presents. It was magnified up to 6,000 diameters, which is 
about as high a power as can be commanded, and still there was not the 
slightest trace of any visible particles. You could not trace the particles, 
but yet you knew they were there. Now that very fluid, after my examina- 
tion had satisfied me that the gold was not discoverable by any visual means, 
was set by in the bottle for a year or two. At the end of that time I found 
that a little sediment had settled at the bottom of the water ; and that sediment 
presented all the appearance of gold dust in a minutely divided state. But 
the water was no longer capable by shaking of being restored to its former 
colour — the bottle merely contained a mixture of visible particles of gold 
with water. Because at first no microscopic investigation could detect the 
particles, it might have been said that they did not exist in the water ; 
but they manifestly did exist there, although the microscope was wholly unable 
to detect their material presence. This is a familiar and palpable example 
of the fact, that molecules or particles of matter not being visible is not the 
slightest evidence of their non-existence. Now it is very important that 
in so valuable a paper as the one now before us there should not be the least 
departure from logical deduction ; but there are one or two points in the 
paper on which I should like to make a few observations. In the second 
paragraph Professor Kirk speaks of life in an object as “ self-movement.” 
Now I should rather take exception to that definition, of the fact of move- 
ment being taken as fundamental evidence of individual life. For example, 
the cells of ciliated epithelium which may be stripped off the back part of 
the throat, will be found under the microscope to consist of little ciliated 
particles, which will move about by ciliary action in the fluid in which they 
are suspended ; but we can no more consider them to be individual organisms, 
or to possess individual life, than we can suppose the effete particles of epidermis 
N 2 
