1864. ] Samug.son on the Source of Living Organisms. 603 
generation,” we shall now enter those of its opponents, and briefly 
consider their investigations. 
In the year 1837 two German observers, Schultze and Schwann, 
endeavoured to show that the germs of infusoria do exist in the 
atmosphere, and that when means are taken to destroy these germs 
before the air in which they are suspended reaches the infusion, no 
animalcule appear in it, even after a lapse of some weeks. By means 
of an apparatus consisting of a flask and tube, provided with bulbs 
which contained sulphuric acid and caustic potash, they submitted the 
air to a kind of purification (from animal germs), before allowing it to 
play upon the infusion ; and they asserted that infusions which had been 
subjected to the influence of air thus treated, showed no signs of animal 
life even after two months’ exposure, whilst others that had been freely 
exposed to atmospheric influences contained innumerable infusoria. 
More recently, Schroeder, a German chemist, arrived at the same 
results by a different method, and one that appears to me to be more 
conclusive ; inasmuch as it might be advanced by the advocates of the 
theory of ‘‘ spontaneous generation ” that the same chemical and physical 
agents (for in some cases the air has been heated to an extreme degree) 
which are said to destroy the germs of living forms in their passage to 
the infusion, might also render the atmosphere unfit to sustain life on 
any terms. Schroeder then* filtered the air by passing it through 
cotton wool, and found that when infusions which had been previously 
boiled were exposed to the atmosphere thus filtrated, no decomposition 
took place. This result he believed to be owing to the fact that 
ebullition destroys the germs which would otherwise be contained in 
the infusion, whilst the cotton wool prevented the access of fresh germs 
with the atmosphere. In this manner he accounts for the preservation 
of fruits, &e., which are boiled and then covered with bladder or other 
materials that serve to filter or exclude the air. 
The experiments of this observer (which have not, I think, been 
sufficiently acknowledged by those who have availed themselves of his 
experience) I have myself repeated with scrupulous care, and the result 
has been that although I cannot fully confirm what he says in regard 
to the entire absence of Protozoa in infusions which have been protected 
by cotton wool, yet I can attest that their numbers and proportions, as 
compared with those in infusions freely exposed to the atmosphere, 
have been so insignificant as to leave me in no doubt as to the truth 
of the general principle which he has enunciated. 
We now come to the researches of M. Pasteur, a French chemist 
of great celebrity, upon whose experiments such stress has been laid 
by certain English and French biologists, that they were regarded 
as having given a deathblow to the doctrine of ‘spontaneous gene- 
ration,” and to have proved beyond a doubt that the germs of protozoa 
are held suspended in the atmosphere. 
Whilst conducting some experiments on the origin of ferments, 
M. Pasteur found in an infusion of yeast, “certain corpuscles, whose 
form, volume, and structure show that they are organized after the 
* ¢«Annalen der Chemie und Pharmacie,’ vol. cix. p. 35. 
