XLII THE ROYAL SOCIETY OF CANADA 
his Belfast address “Trace the line of life backwards and see it appa 
more and more to what we call the purely physical condition.” 
“T prolong the vision backward across the boundary of ner 
evidence and discern in ‘matter’ the promise and potency of every 
form and quality of life.” 
The closing paragraph of Le Dantec’s “Elements of Philosophical 
Biology” discloses a sanguine attitude to this question. “Le monde 
savant est aujourd’hui tellement préparé à cette découverte, que 
l’annonce prématurée de la réalisation d’une génération spontanée dans 
de la gelatine soumise à l’action du radium n’a surpris personne. Quand 
la synthèse effective sera obtenue, elle n’étonnera pas; elle sera d’ailleurs 
parfaitement inutile; car, avec les connaissances nouvellement acquises 
par les savants, it n’est plus nécessaire à un esprit éclairé de voir fa- 
briquer du protoplasma, pour être convaincu de l’absence de toute 
différence essentielle, de toute discontinuité absolue entre la matière 
vivante et la matière brute.” 
A continued study of the smallest forms of life led to various 
improvements in the microscope, such as the introduction of homo- 
geneous immersion lenses, better arrangements for condensing the 
light employed and the invention of new kinds of glass. The two 
former were really the invention of English amateur microscopists, 
but were practically introduced into general use by the Zeiss firm in 
Jena, where, with the co-operation of the Professor of Physics in the 
University, the highest scientific attainments were united with the 
highest technical skill. It is to such co-operation that Germany owes 
its present position in the scientific and industrial world. 
The theoretic limit of visibility by the microscope is one-quarter 
of a micron. It is just possible with the best apparatus to distinguish 
lines which are no further apart, but particles 20-30 times as small 
can still be seen by the ultra-microscope, an invention also perfected 
in Jena in recent years. Its principle may be explained by recalling 
the visibility of dust particles in a dark room when one is looking at 
right angles on a beam of sunlight streaming into it. So in the ultra- 
microscope one does not see the image of the object as in direct micro- 
scopic vision but merely the cone of light diffracted from it, and although 
no conclusions can be formed as to the shape or structure of such 
objects, nevertheless the number, size and grouping of particles may 
be studied. 
, MARINE BrIo.oey. 
The microscopic creatures which I have been dealing with hitherto 
are parasitic, but there exist free-living creatures of similar size, the 
importance of which has only been recognized within the period dealt 
with. I refer to the microscopic plankton or floating organisms of 
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