946 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’ 
F is the Leptothriz’* always found on the human teeth: and 
Fig. G is unquestionably a spirochaete—probably the so-called 
“ Spirochaeta buccalis”.” The figures obviously represent 
bacteria, and include no protozoa; and nowhere but in the 
mouth is such an assemblage of forms to be found. When 
Leeuwenhoek’s own words are considered in conjunction with 
these illustrations, the interpretations just advanced must 
surely be self-evident to everybody who studies the microbes 
of the human mouth “ with the help of a good microscope.” 
Yet ever since the foregoing observations were recorded 
they have been misinterpreted—and even questioned and 
denied—in the most astonishing manner. It is unnecessary 
to chronicle here all the wild assertions that have been made 
in this connexion.’ 'T'wo of the most recent comments will 
serve as illustration : 
(i) Singer (1914) reproduces the figures from the Phil. 
Trans. 1684 (misdated by him 1683), and says that figs. A, F, 
and G [the spirochaete] are all ‘‘rod-shaped organisms ”’ 
[meaning bacilli?]; and that B [Selenomonas| is “a flagellated 
organism” [meaning a protozoon?]|. He even recognizes 
‘ sarcinae’”’ in Leeuwenhoek’s description: but the figure * so 
strangely interpreted is said by Leeuwenhoek himself to 
represent epidermal scales from the human skin, as seen 
under a low magnification. 
(ii) Wenyon (1926), discussing the Trichomonas of the 
human mouth, says “it is probable that Leeuwenhoek saw 
the flagellate in the tartar of his own and other people’s 
teeth.”°’ Although no reference is given to the passage in 
' Leptothrix buccalis Robin, 1853: Bacillus maximus buccalis Miller, 
1890. 
| 7 specific designation commonly ascribed to Cohn. But see Dobell 
1912). 
* I must mention, however, that Robin (1853, pp. 352-354) made a 
careful study of the Latin versions of Letter 39, and correctly identified the 
Leptothrix. Ue also recognized Fig. B as a “vibrion”’. Beijerinck (1913, 
p. 10, note) wrongly supposes that Ldéffler (1887) was the first to direct 
attention to L.’s pictures of bacteria in the human mouth. 
* Fig. H—which occurs in the same letter, but is not reproduced here. 
To my mind this figure bears no resemblance to a Sarcina or any other 
bacterium : and of course no Sarcina lives normally in the mouth of man. 
° Wenyon (1926), Vol. I, p. 656. So far as I am aware, there is no 
passage in any of L.’s writings which can be plausibly interpreted as an 
account of the Trichomonas of the human mouth. 
