LETTERS TO HOOKE AND CONST. HUYGENS 187 
Zuylichem.* And I feel bound to say, furthermore, that 
last Friday evening I took some pepper-water, in which 
there were many living animalcules, and mixed it with 
about a like amount of rain-water, wherein I had put a 
quantity of pounded ginger: and forthwith examining 
this mixt water, I found that the animalcules were slow 
a-moving. Some hours afterwards, examining this water 
anew, I could perceive no animalcules whatsoever in it : 
but about twice 24 hours afterwards, I saw very distinctly 
some animalcules which I judged to be a hundred million 
times smaller than a sand-grain, but without being able 
to discern any of those animalcules that had been before 
in the pepper-water.” 
The enclosed letter to Constantijn Huygens, dated 20 May 
1679, I shall now give in full. The original, from which it 
was copied, is preserved among the Huygens manuscripts at 
Leyden *—the following being a complete translation of the 
copy sent to Hooke: 
Along with this goeth my calculation, which I confess 
is quite imperfect, seeing that my estimates were made 
by the eye alone. 
I have oft-times let my thoughts run on the extreme 
small vessels and sinews* wherewith the very little 
* The father of Christiaan Huygens the astronomer and mathematician— 
not his elder brother. Cf. p. 42, note 2, supra. 
* It is probable that the animalcules in the pepper-water were protozoa 
of some sort, which were killed when the ginger-water was poured upon 
them: while the very minute forms which developed in the mixture after 
48 hours were evidently a new crop of bacteria. 
* See Haaxman (1875), p. 136,—where the date is given as 21 May 
1679: but L.’s copy, sent to Hooke, is by himself dated May 20, as stated 
above. The copy was made with his own hand.—The original has recently 
been printed in full in Guvr. Compl. de Chr. Huygens, VIII, 168-172 (also 
there dated May 21). 
* Or “nerves”: MS. senwwen. Zenww nowadays means a nerve—as it 
often did to L.—but at an early date it also meant a sinew (tendon), and 
from what follows this seems to be the correct rendering here. (Cf. the 
original meaning of Lat. nervus and Gr. vedpov.) 
