PRESIDENT’S ADDRESS TO MANCHESTER MICRO. SOCIETY. I0I 
aid in distinguishing human blood from that of several domestic 
animals, viz., the horse, ox, pig, sheep, and goat. ‘These tests, 
in combination with exact measurement of the corpuscles, are 
powerful aids in medico-legal investigations, in deciding the nature 
and source of a suspected stain, and may also be valuable in 
detecting some forms of imposture. That form of deception 
known to the medical profession as “ malingering” has been 
revealed by the microscopical examination of the supposed san- 
guineous expectoration of a suspected patient. Many years ago, 
Dr. J. H. Bennett found in the sputum of a woman the blood of 
a bird, to the use of which she afterwards confessed. 
You are all aware of the aid which the practice of medicine has 
derived from the microscope in the investigation of the nature of 
disease, and the diagnosis of its special forms. As the know- 
ledge of the real relation between structure and function in health 
is due to microscopical research, so also is that between deranged 
structure and the symptoms of disease. I hope I may be excused 
for invading the province of our medical friends in order to 
call your attention to some of the latest researches that affect 
their art. It is not many, years since Bacteria, those minute 
living organisms which appear to spring into existence in fluids 
containing organic matter undergoing putrefactive change, were 
regarded more in the light of microscopical curiosities, or as tests 
for an object-glass, than as having any scientific importance. 
Observers were, however, at work upon these and _ similar 
organisms, endeavouring to decide the question of the possibility 
of spontaneous generation. After a series of experiments on 
various nutritive fluids in flasks hermetically closed after boiling 
Dr. Bastian wrote a work to prove that he had discovered this 
form of generation. More careful experiments conducted by 
Pasteur, Tyndall, Dallinger, and others have shown this view to 
be untenable. Dr. Tyndall found that the germs themselves 
resisted the most prolonged boiling, but that if intervals of a few 
hours were allowed to elapse after each of several boilings of a 
single minute the fluid remained sterile. The living organisms 
could be killed only as they assumed the adult form, and as the 
germs were of different species, and in various conditions of activity, 
they required to be attacked separately. About the year 1838 
Schwann was engaged in a similar investigation, when he dis- 
covered the vital nature of the changes in the cells of yeast, and that 
certain forms of fermentation and putrefaction were dependent 
upon the presence and increase of living organisms. The 
chemical theories of Liebig for a long time threw discredit upon 
the observations of Schwann, until Pasteur repeated them, and 
performed others, with the result of showing that each kind of 
fermentation that is not the result of purely chemical reactions 
