NOTES AND MEMORANDA. 
33 
tliink Colin is justified in separating the two genera) of Dujardin * are 
distingaislied by the greater regularity and closeness of the curves of 
the spiral, and their uniform corkscrew motion. The distinguishing 
character of the flexibility or rigidity of the threads in the genera 
SpirochEeta and Spirillum respectively, insisted upon by Ehrenberg 
and followed by Cohn, is rightly set aside by Dujardin as superfluous. 
All the Spirilla, of which Cohn gives three species— /S^. tenue, S. undula, 
and S. volutans — were found by him in the decomposing tissues of a 
fresh-water snail. They are distinguished mostly by their size from 
each other. The >S^. volutans is by far the largest of all the bacteria, 
if we apply the name to the genus at all. It is thus described by 
Ehrenberg, " Filis valde tortuis robustis et elongatus." Cohn fancies 
that he has found traces of organization within it. 
He states that having above given a short resume of the labours of 
the most trustworthy naturalists upon the morphology of bacteria, he 
will now only add a few remarks upon the limitations we should place 
on the term. 
In the first place, then, it seems right to consider bacteria as 
strictly forming part of the vegetable kingdom, and this, as I have 
before remarked, is the opinion of all the most trustworthy authorities 
of France, Germany, and Italy. I should have included our own 
country in this geographical list had I not lately been somewhat 
startled to find a learned Professor in a recent lecture at the Royal 
Institution j reported to have represented bacteria to be " animal- 
cules." Secondly, I think the name bacteria ought to be restricted to 
those minute rod-like hyaline bodies, the B. termo and B. lineola of 
Cohn. They have a more or less rapid to-and-fro motion. The so- 
called " locomotive bacteria " of some physiologists are probably in 
many instances specimens of the larger V. regula. Eivolta considers 
that the true bacteria have no proper locomotive powers, only the 
vacillatory movements common to all small particles of matter sus- 
pended in liquids. Thirdly, we must, I think, always associate the 
presence of the true bacteria (especially the B. termo) with putre- 
factive or analogous changes in organic liquids. 
At some future period I hope to give a short account of the etiology 
of these organisms, and the part they play in the causation of disease. 
NOTES AND MEMOEANDA. 
The Society's Universal Screw. — We quote the following re- 
marks from ' Science Gossip,' as they are of some importance. They 
are made by M. A. de Sonza Guimaraens. There is a general com- 
plaint among microscopists respecting the so-called " universal 
screw." I have myself felt great annoyance when finding that the 
screw is not universal. Some of my friends' object-glasses (having 
the " universal screw ") do not screw home in the nose-piece of one 
* ' Infusoires,' p. 209. 
t See report in 'Illustrated London News,' Feb. 14, 1874, p, 162. 
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