399 
G. H. F. Nuttall 
others are preserved among the MSS. in the Library of the Society. In 1680 
he was elected a Foreign Member of the Royal Society. 
He made numerous observations of broad biological interest, amongst 
many things discovering the spermatozoa and demonstrating the capillary 
circulation. He made important contributions to parasitology. He described 
free living Protozoa (1676) and was the first to discover parasitic Protozoa, 
for, in a letter dated 4 Nov. 1681, to Robert Hooke, Secretary of the Royal 
Society, he gave a brief but unmistakable description of Giardia (Lamblia) 
intestinalis which he obtained from his own stools when loose after errors in 
diet(7). In his letter of Sept. 1683, and 16 Oct. 1692, he described the dis¬ 
covery of minute motile organisms ( Bacteria ) in the “materia alba” from 
between his teeth. Not only was he the first to discover bacteria but he was 
the first to figure them(i, 3). He appears to have been the first to raise 
Pediculus humanus experimentally, doing so upon his own person. He also 
studied the mechanism of feeding (4, 6) and the structure of the mouthparts 
of the louse, and in 1697 he described and figured nits (2). Of his work on Pulex 
irritans my late friend Professor H. 0. Plimmer, F.R.S.(5) wrote: 
“ He glorified even in the common flea—so carefully collected for him by his 
little maidservant—and made the first exact observations upon this enemy 
of man. He described its structure and traced out the whole history of the 
metamorphoses of ‘this minute and despised creature,’ which some asserted 
to have been produced from sand, dust, dung of pigeons, or urine; and he 
showed that it was ‘ endowed with as great perfection in its kind as any large 
animal.’ He also found that its pupa was attacked by a mite, the knowledge 
of which fact gave rise later to the well-known lines of Swift (1667-1745): 
So, naturalists observe, a flea 
Has smaller fleas that on him prey; 
And these have smaller still to bite ’em, 
And so proceed ad infinitum .” 
The two portraits reproduced in our plate were photographed by me in 
Gottingen in 1893 from the frontispieces to the 1695 and 1719 editions of 
Leeuwenhoek’s works. The first shows him at the age of 63 (1695), the legend 
on the frontispiece reading “ Antonius a Leeuwenhoek Regiae Societatis Lon- 
dinensis Membrum....J. Yerkolje pinx. A. de Blois fee.” The second portrait 
(1719) shows him in his old age, the head being in an oval bearing an inscrip¬ 
tion and held above the clouds by a trumpeting angel of fame; this frontis¬ 
piece bears various allegorical figures, statues, and a distant view of Delft in 
the background. His monument at Delft, which I visited in 1893, bears a 
medallion in marble; the head is shown in profile, the forehead being traversed 
by very deep wrinkles which long years of work with microscopes must surely 
have helped to chisel! 
% 
References: (1) Leeuwenhoek (1695), Arcana Natura Detecta, Delphis Batavorum, pp. 
41-46, 53, pi. opposite 192, 187, 335-338 and pi. (2) Leeuwenhoek (1697), Brieven, p. 204 and 
pi. (3) Leeuwenhoek (1719), Epistolae physiologica super compluribus naturae arcanis, etc. 
