384 ON THE LACTIC FERMENTATION 
or two, minute bacteria had shown themselves in a drop withdrawn from it, 
and applied between the immersion lens and the glass that covered the object. 
Along with the drop I had, no doubt, taken a portion of a bacteric film on the 
surface. Adult bacteria, therefore, do, as a matter of fact, exist, though it 
may be in a very minute condition, as a scum on still water, and there can, 
therefore, be no reasonable doubt that they exist also disseminated through 
moving water, but detached from one another by the motion of the liquid, 
so as no longer to present the recognizable characters which they have, even 
though extremely minute, when packed together in the form of a scum.t. And 
supposing them present, thus minute, motionless, and isolated, and as widely 
scattered as our experiments proved them to be in the water investigated, any 
attempt to search for them with the microscope would be, I do not hesitate to 
say, absolutely hopeless. 
Our morphological knowledge is also opposed to the idea that bacteria 
should have germs related in point of magnitude to the adult organism as the 
seeds of a poppy or the spores of a fern are to the full-grown plant. It is true 
that there are some species of bacteria in which appearances have been seen 
that appear to indicate the existence of spores, notably in the case of the Bacillus 
anthracis, which seems to constitute the virus of malignant pustule.2 But in 
all such cases the supposed spore or germ is not only conspicuous from its highly 
* The minute form in which the Bacterium lactis was found in milk much diluted with water is 
only an extreme degree of what was seen under other circumstances. It has been before mentioned 
(p. 374) that as the souring of milk proceeds the bacteria assume a smaller size. Also when growing 
in urine, though they presented in the early days the same dimensions as in milk, they were found much 
smaller at a later period, though still proved by experiment to retain the property of inducing the lactic 
fermentation in milk. Again, the Bacterium lactis which has been described as growing slowly in 
Pasteur’s solution at the expense of a little piece of curd, was almost as small as that in the milk diluted 
with water. The puny character of the progeny depends probably upon unsuitable or inadequate 
supply of nutritious material ; and in comparison with the media in which bacteria ordinarily thrive, 
the elements for their nutrition are extremely scanty in water. Again, as regards moving bacteria, 
it is a very common thing to see them become, not only of smaller size, but motionless as they continue to 
develop in one and the same medium. A good example of this in a bacterium of unusual form is given 
in the paper in the Microscopical Journal before referred to (p. 17 and Plate XIX; p. 321 and Plate XI 
of this volume). Itis, therefore, not surprising that moving bacteria should, asa rule, acquire motionless 
as well as minute characters in water. At the same time it is easy to understand that some particular 
bacteric species, like multitudes of algae and infusoria, may have water as their favourite habitat, and 
attain in it their largest dimensions. 
* See especially a memoir recently published in the Quarterly Microscopical Journal (vol. xvili, new 
ser.), by Dr. Ewart, who has observed that the highly refracting bodies which form in the threads that 
constitute the organism become free and afterwards multiply by segmentation, and that the individuals 
which result from this fissiparous proliferation again give origin to threads. M. Pasteur describes highly 
refracting spots, which he believes to be of the nature of germs, in some other bacteria (Etudes sur la 
Biére, p. 295); and I have myself seen what I have regarded as nuclei in the finely granular protoplasmic 
mass of some large bacteria, and I have sometimes observed the threads cleared of granular material, 
as if the nuclei were on the point of becoming free, appearances corresponding so far to those in the 
Bacillus anthracts. 
