GERM THEORY OF FERMENTATIVE CHANGES 333 
was milk converted into so viscid a material as it was under the influence of 
that organism, simply because other organisms which would have interfered 
with the viscous fermentation were for the first time excluded. 
I have dwelt at what will, I fear, be thought tedious length upon this dis- 
cussion, because the conclusion arrived at seems to me of extreme importance. 
For if the same bacterium may, as a result of varied circumstances, produce 
in one and the same medium fermentative changes differing so widely from 
each other as the formation of lactic acid and that of black pigment in milk, 
it becomes readily conceivable that the same organism which under ordinary 
circumstances may be comparatively harmless, may at other times generate 
products poisonous to the human economy. We can understand, for instance, 
a thing that has at an earlier period of my practice as a surgeon often puzzled 
me, though now, happily, under the antiseptic system of treatment, I never 
have occasion to witness it, viz. the development of hospital gangrene beneath 
dressings left for a long time unchanged, whereas in the same hospital ward 
sores dressed daily continued healthy. Assuming what analogy leads us to 
suspect, that some organism is the cause of the disease, why should the special 
virus of hospital gangrene become introduced into a sore under the former 
condition more than under the latter? We now see that it is not essential to 
assume the existence of a special virus at all, but that organisms common to all 
the sores in the ward may, for aught we know, assume specific properties in 
the discharges long putrefying under the dressings. Similarly, we can imagine 
the unhealthiness of an old uncleansed hospital as caused not by the intro- 
duction into it of new organisms, but by a modification of those common to it 
and to freshly built institutions. I take these illustrations from surgery ; but 
to the medical reader others of equal importance will readily suggest themselves 
from physic. 
Another peculiarity of the glass of Pasteur’s solution remains to be men- 
tioned besides the formation of pigment in it, viz. a putrid smell which I never 
observed before in that fluid, and at the same time, a remarkable taste, a com- 
bination of slight bitterness with astringency, the latter so marked as to lead 
me to test for gallic or tannic acid with a persalt of iron, though without effect. 
Admitting then that we had here to deal with only one bacterium, it pre- 
sents such peculiarities both morphologically and physiologically as to justify 
us, I think, in regarding it as a definite and recognisable species for which I 
venture to suggest the name Bacterium lactis. This I do with diffidence, believ- 
ing that up to this time no bacterium has been defined by reliable characters. 
Whether this is the only bacterium that can occasion the lactic-acid fermenta- 
tion, I am not prepared to say ; but it seems most unlikely that any other kind 
