LETTER 39. INTERPRETATIONS 945 
prepared, and this was inserted in the Latin translation which 
appeared subsequently. The still later omission of Fig. G 
from the second Phil. Trans. version was probably merely a 
consequence of the great condensation which this very short 
and faulty translation underwent at the hands of its editors. 
Some such explanation would readily account for the 
variations in the different versions. But in any case, I think, 
we need not hesitate to accept the final and complete set of 
drawings published with the Latin letter—drawings which 
Leeuwenhoek must himself have seen and passed for press. 
The omission of Fig. G from the Dutch edition was certainly 
unintentional, as it is referred to in the letterpress. 
It is not possible to doubt, after reading the foregoing 
descriptions and inspecting the pictures, that Leeuwenhoek 
discovered ‘the bacteria in the human mouth: for he described 
—and described recognizably—all the most characteristic 
forms occurring in this situation. To anybody familiar with 
these organisms his figures speak so clearly that his words are 
almost superfluous. If I were shown these sketches for the 
first time, and asked to interpret them, I should be able to 
say—after only a moment’s reflexion—what they probably 
depict. Fig. A is a Bacillus: Fig. B shows the peculiar 
organism known as “ Spirillum sputigenum” :° Fig. EK shows 
some of the Micrococct commonly present in the mouth: Fig. 
"IT must note that priority for this discovery has been claimed for 
Hartsoeker: but this is due to a misunderstanding. The true story can 
be pieced together from L.’s writings and Hartsoeker’s own words (1730). 
Hartsoeker, knowing of L.’s discovery of the spermatozoa, tried to pass it 
off as his own: but he says that he was ashamed to tell people that he had 
examined semen with the microscope, and therefore told them at first that 
the “ animalcules’’ which he had found in it were in the saliva. But he 
further says, quite definitely (1730, p. 6), that he never really saw any 
animalcules in saliva, and he attempts to discredit L.’s discovery. He 
regarded it as an invention. Consequently, Hartsoeker himself never 
claimed to have found any organisms in the human mouth, and even 
denied their existence. 
2 So named by Miller (1890). This organism is not really a Spirillwm 
at all, but belongs to the genus Selenomonas Prowazek, 1913a. I have 
studied it (in pure culture) but I have seen no accurate description of it.— 
In the genus Selenomonas the flagella arise from the concave surface of the 
arched or crescentic body—not from its ends, as in Spirillum. Their 
lashing produces the curious whirling motion observed by L. Although the 
text-books of bacteriology are usually silent on the subject, I can say from 
my own knowledge that Selenomonas sputigena is very common in human 
mouths—and very difficult to isolate in cultures. 
