366 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS”’ 
read all his works (which is probably impossible and would 
certainly be unprofitable), but only some parts of those which 
deal with biological topics. In none of them can I find any 
evidence whatsoever to indicate that he ever saw or described 
either a protozoon or a bacterium. But others believe that 
they have been more fortunate, so I must briefly consider their 
findings. 
The first person to credit Kircher with the discovery of 
the Bacteria was, I believe, Friedrich Léffler (1887), who 
opens his work on the history of bacteriology with a quotation 
from the Scrutinium Pestis (1658)* wherein Kircher says: 
“That air, water, and earth are swarming with countless 
insects, is so certain that it can even be proved by ocular 
demonstration. It has hitherto also been known to everybody 
that worms swarm out of rotting bodies: but only after the 
wondrous invention of the Microscope did it become known 
that all decomposing things swarm with an innumerable 
brood of worms invisible to the naked eye: which even I 
myself would never have believed, had I not proved it by 
repeated experiment over many years.” * 
Now this passage contains no obvious reference to any 
organisms other than worms or insects—well known to 
everybody at the time when Kircher wrote: yet for reasons 
unexplained Léffler alleges that it “announces . . . the 
discovery of a new world of living creatures” —by which he 
means, presumably, the Bacteria. But does it? Surely not. 
The assumption is so far-fetched, indeed, that Léffler felt 
constrained to add that ‘“ Kircher was unable to give any 
more accurate data regarding these worms;” and he then 
made an irrelevant reference to the Ars Magna Lucis et 
Umbrae (1646). Any ordinary person would conclude that 
Kircher never described bacteria for the simple reason that 
he never saw them—and because Leeuwenhoek had not then 
1 Léffler actually quotes (in German translation) from an edition of 
1671, but gives no exact reference to the passage. I have not seen this 
edition, but it appears to be a reprint of the first Leipzig edition (1659), 
which I possess. In this the passage quoted (from Cap. VII, § II) is on 
p. 69. I have to thank Dr Singer for kindly lending me his own copy of 
the original edition of 1658. 
2 T translate from the original dog-latin of Kircher (1658)—not from 
Loffler. 
