436 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vor. VIII: 
That such ultramicroscopic forms of life exist we know in a few 
cases at least. Beijerinck in his study of the disease of tobacco leaf 
found that the causative element could not be seen with the highest 
powers of the microscope and that it was minute enough to pass through 
the pores of a Chamberland filter. That the disease is due to a micro- 
organism and not a ferment other facts determine beyond doubt. 
Further, the consensus of opinion amongst those who have carefully 
investigated the question is that yellow fever is due to a micro organism 
which is ultramicroscopic and it is possible that the pathogenic agent 
in rabies is also an organism that is beyond the limits of microscopic 
vision. 
It is not necessary to multiply instance, it suffices for our present 
purpose to note that there are to-day organisms which consist practi- 
cally of suspension particles constituted of a few molecules aggregated 
as in the case of each protein particle in suspension in a “solution” of 
white of egg, and that these molecules in each single isolated particle 
carry on the functions which we usually group under those of life. 
When in consequence we seek to explain the origin of life, we do 
not require to postulate a highly complex organism such as we can see 
even with the low power of the microscope, as being the primal parent 
of all, but rather one which consists of afew molecules only and of such 
a size that it is beyond the limits of vision with the highest powers of 
the microscope. Such an organism would be the smallest unit of life 
and it might be supposed that protoplasm arose from aggregation of 
such units, each more or less differentiated from its fellows, just as the 
higher or multicellular forms of life have arisen by aggregation of cells 
which have differentiated more or less, thus giving rise to differences of 
function in the different parts. 
The question which we now must face is this:—Did conditions 
ever exist in the history of the globe which favoured the production by 
natural means of such ultramicroscopic organisms? The answer which 
I would make to this question is an affirmative one. 
According to the Nebular Theory a great many constituents of the 
rock crust of the globe such as carbon monoxide, carbon dioxide, chlor- 
ine, phosphorus as phosphoric pentoxide, sulphur as sulphur dioxide and 
trioxide, potassium, sodium, calcium, magnesium, as well as all the 
water on the globe, were, when the earth was cooling down from 1200° C. 
to goo® C., in the atmosphere, the pressure of which on calculation was 
greatly over 270 times that of our atmosphere. As the temperature 
a 
