1903-4. | ULTRAMICROSCOPIC ORGANISMS. 5S 
ULTRAMLECROSCOPLC? OR GANTS MS: 
By J. J. MACKENZIE, B. A., M. B. 
(Read 30th January, 1904.) 
Wits the discovery of bacteria and the demonstration of their form 
and dimensions by the older bacteriologists, the question very early arose 
as to whether, with the recognition of these minute forms of life we had 
reached the limits of size of organized beings or whether there were not 
smaller organisms yet which we had not seen or could not see because of 
their minuteness. This question became the more pressing, the more we 
sought in vain for the organisms which caused such diseases as scarlet 
fever, measles, small pox, rabies and many other forms of infection; and 
the idea was frequently expressed that there must be forms of life smaller 
than the smallest known bacteria, so small in fact, that they probably 
were beyond the range of microscopic vision, and that on this account we 
have failed to find the parasites of these diseases. In regard to bacteria 
a striking fact may be noted in the remarkable uniformity of size of the 
various members of the group. They vary, it is true, enormously in the 
length of their cells or cell complexes, but in regard to the thickness of the 
cell or the diameter of globular forms, individual members of the group 
vary very slightly from an average of I.0 micron to 1.5 microns. If we 
take one of the largest as an example, called on account of its size bacillus 
megathertum, we find that its width does not exceed 2.5 microns, whilst 
the smallest of the disease-producing forms, the bacillus which causes 
epidemic influenza, has a length of 1.2 microns and a width of 0.4 micron. 
Recently Erwin von Esmarch has described a putrefactive spirillum from 
water which is 1.3 microns long and o.1-0.3 micron wide, the smallest of 
the bacteria which has ever been cultivated. 
The possibility of demonstrating the existence of organisms which 
are too small to see with the strongest microscope would seem to be a 
difficult problem, and so it is, and we consequently cannot proceed to the 
demonstration by ordinary methods of bacteriological research. It has 
been necessary to adopt certain what might be called extraordinary 
methods to give evidence of their existence. 
Fortunately for the success of the demonstration, those which have 
so far been discovered are all parasitic and consequently experiments can 
be made by animal inoculation and the presence of the hypothetical para- 
sites demonstrated by the disease produced in the animal. In addition 
to this, however, we have in the laboratories, filters which can successfully 
