LETTER 88. 16 guLy 1683 931 
with the other matters mentioned that it is not always easy to 
separate them. The passages in question—omitting irrelevant 
details (duly indicated)—are as follows:! 
The first frog that I dissected sat in the road; and it 
seemed so weak from the cold,’ that though I gave it a 
bit of a kick on with my foot, it didn’t jump away. When 
I picked it up and opened it, I found ’twas a female, in 
whose guts there were worms, which had the shape of 
those worms that children void in their stools.’ These 
worms * were about as thick as a hair off one’s head.’ 
But what most surprised me was, that I observed in the 
blood (which had run out of the many blood-vessels that 
Thad cut, into the clean ° dish in which I dissected the frog) 
a great number of living animalcules,’ which were about 
" From Letter 38, 16 July 1683 [N.S.]. To Christopher Wren. 
MS.Roy.Soc. Read at a meeting of the Society held on July 18 [0.S.] — 
not on July 11, as appears (owing to omission of a date) in Birch, Vol. IV, 
p. 215. Published in Brieven, Vol. I (Dutch) ; Opera Omnia, Vol. I (Latin). 
The Dutch version first appeared in 1685 (Ontled. en Ontdekk.), and the 
first Latin version in the same year (Anat. et Contempl.). In both of these 
the letter is dated correctly : but in the Op. Omn. (and in the earlier Anat. 
s. Int. Rer. [1687], which contains a 2nd edition of the Latin letter) it is 
misdated July 26. A short English translation was published in Phil. 
Trans. (1683), Vol. XIII, No. 152, p. 347; and this was therefore the first 
version to appear in print. Hoole also translated a part of this letter, but 
not that which here concerns us. My translation is based primarily upon 
the original MS. 
* In a previous (untranslated) paragraph it is noted that these frogs 
were studied on 1 April 1683, when they were coupling. It is thus certain 
that the species was Rana temporaria—not R. esculenta, which breeds later. 
* Probably meaning Oxyuris (=Enterobius) vermicularis. 
“The “worms” found in this frog were obviously not protozoa or 
bacteria but nematodes; and— if the foregoing identification of Oxywris be 
correct—they were probably Ozysoma brevicaudatum, which is very 
common in R. temporaria. 
° A description of the blood-corpuscles of the frog is here omitted. 
° schone printed version. Not in MS. 
" When all the particulars related are taken into account—size, host, 
origin, movements, etc.—I think there can be very little doubt that this 
‘animalcule”’ was Trichomonas (or Trichomastia ?) batrachorum. 
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