THE RELATION OF THE LABORATORIAN TO THE PRACTITIONER. 
175 
Ehrenberg, between the years of 1795 and 1875, with the 
improved microscope and lenses at his command, prepared the 
first logical classification of bacteria. He differentiated the true 
bacteria from the protozoa, and his arrangement is the basis for 
the classification used most extensively at present. 
Between the years of 1828 and 1898 Cohn elaborated and 
modified Ehrenberg’s classification. With the continued im¬ 
provement in the microscope and laboratory technique, more 
careful studies of structure, form and relationship have been 
rendered possible, and many classifications and groupings for 
bacteria have been sugg*ested. 
The present classifications of bacteria is by Ungula and is 
a very complex one and which would require too much time and 
space to give it in detail here. 
In ancient times and as far down as the Middle Ages it was 
generally held by the philosophers and scientists that living 
things, animals and plants could arise de novo. 
Among the first observers that disproved this theory and 
created doubt in man’s mind as to the validity of spontaneous 
generation, or the creating of life without life, or as known 
to-day as the Abiogenisis theory, was Francisco Redi, who 
carried on an experiment by covering meats with gauze to pro¬ 
tect it from flies and found that maggots did not develop in it 
spontaneously, but instead arose from the eggs which the flies 
deposited on the screen. This formed a path of light and similar 
studies were carried on to a much larger degree and in conse¬ 
quence it was not long before the idea or belief of spontaneous 
generation of the higher forms of life was abandoned. 
When the new improved microscope revealed the presence 
of myriads of micro-organisms in all decaying or putrefying 
materials, it was concluded that these organisms arose without 
progenitors of their own kind, but directly from the organic 
material of their surroundings.. 
Boiling at that time in history was believed to surely destroy 
all life, yet it was found by the scientific observers of that time 
that boiled decoctions would not always remain free from micro- 
