LETTER 18. PEPPER-WATER 141 
yet these animalcules swam as well backwards as forwards, 
though their motion was very slow. And were I to 
contrast these creatures with the eels or worms which are 
in vinegar,’ I imagine the proportions would be thus : 
As a worm of the bigness of a big pin, is to an eel of 
the thickness of one’s wrist : So are these very little living 
creatures or eels in the pepper-water, to the size of the 
eels in vinegar. 
5th Observation [on Pepper-water]. 
On August the 2nd, in the evening about 7 o’clock, I 
again examined my well-water, which was very clear 
(especially when it stood in a kettle or pot; but standing 
in a clean glass, alongside of clean rain-water, the rain- 
water outdid the well-water in clearness). In this well- 
water I saw living a great many of the oft-mentioned 
very little animalcules*; some thousands, indeed, in one 
drop of water. I then poured some of this water into a 
porcelain tea-cup, adding thereto a quantity of coarsely 
pounded pepper; and [I stirred round the pepper in the 
water, deliberating whether the said animalcules would 
remain alive in the peppery water, or whether they would 
die. This water and pepper having been stirred up, I 
examined it, and saw the animalcules living: after the 
lapse of half an hour I examined it again, and saw the 
animalcules still alive, but their motion was not so quick 
as when they were in plain well-water. After the lapse 
of two hours more, examining the water again, I saw the 
ee ee 
1 A yemarkably shrewd observation, which proves conclusively that L. 
was here dealing with bacteria. The organisms were evidently the long 
flexible thread-bacteria (Pseudospira C.D.) so common in infusions. 
2 Of these more anon. The “vinegar-eel” (Anguzllula acett) was 
described by L. in an earlier letter, dated 21 April 1676. See Phil. Trans., 
Vol. 0%, p: 6093 (1676). Power, Kircher, Borel, and others had, however, 
discovered this organism at a still earlier date, though L. was apparently 
unaware of their observations. IL. gives figures of the eel in a later letter 
(No. 43, 5 Jan. 1685). 
® fe., bacteria, in all probability. 
