ON THE RELATIONS OF MICRO-ORGANISMS TO DISEASE 397 
referred to, it occurred to M. Pasteur that it might perhaps be the oxygen of 
the air admitted to the vessels. Oxygen is essential to the growth of the organ- 
ism, but it might, as M. Pasteur thought, be, nevertheless, in long-continued 
action upon it, a cause of weakness. With a view of testing this idea he insti- 
tuted cultivations of the bacterium in broth contained in tubes partially filled 
with the liquid, that is to say, containing a certain proportion of their volume 
of air, but sealed hermetically. The result was a growth of the organism, indi- 
cated by turbidity of the clear fluid, attaining a degree proportioned to the 
amount of air present in the tube, but coming to an end when that air was 
exhausted, so that the little organism, no longer growing throughout the liquid, 
fell to the bottom of the vessel, leaving the fluid again clear. The organism 
having now exhausted all the free oxygen, was from this time forth presumably 
protected from the influence of that element, and, in exact accordance with 
M. Pasteur’s theory, it was found that no matter how long these closed tubes 
were kept, the organism retained not only its vitality, but its full virulence, as 
tested by inoculation of healthy chickens.’ 
There can be no question as to the great importance of these facts; and 
the medical world must for ever remain deeply indebted to M. Pasteur for 
eliciting them. Doubts may, however, be entertained regarding the inter- 
pretation of the phenomena. Thus Dr. Greenfield, whose own researches have 
had special reference to the modifying influence exerted upon bacteria by the 
medium in which they grow, has thrown out the suggestion that the enfeeble- 
ment of the organism of fowl-cholera growing with free access of air may be 
due to alterations in the fluid which they inhabit rather than to the effect of 
oxygen upon them. When free access of oxygen is permitted, the organism, he 
contends, will continue to grow till all the material suitable for its nutrition is 
exhausted, and as the nutriment becomes defective the progeny will be feeble. 
At the same time this exhaustive development of the organism will be attended 
by the full measure of possible alteration in the quality of the liquid which the 
srowth of the organism can effect, and this alteration will naturally involve the 
production of substances which may exert a prejudicial influence upon the 
organism itself. On the other hand, the bacterium, when growing in a sealed 
tube with limited supply of oxygen, has its development brought to a stand 
by the exhaustion of that gas, while the organism is in full vigour and in a fluid 
but slightly changed from its original wholesome condition. It thus remains 
like a vigorous seed, ready to start into energetic growth when the conditions 
for its germination are supplied.2, The essential difference between the two 
1 See Comptes Rendus, October 26, 1880. 
2 See ‘ The Brown Lectures’, by W. S. Greenfield, M.D., &c. ; Lecture II, Lancet, January 1, 1881. 
