C. Dobell 
347 
on this point, and so far as I can discover Leeuwenhoek nowhere published 
any further observations on the bile of rabbits, though he records many other 
observations made upon these animals—both wild and tame. I mention these 
points for the following reason. It might be said that had Leeuwenhoek really 
studied a rabbit suffering from coccidiosis, then he ought to have noted the 
lesions—visible to the naked eye—in its liver. To this I would reply that what 
evidence there is points to the conclusion that his animals were not heavilv 
infected, and in such animals it often happens that no superficial lesions are 
visible to the naked eye, even though oocysts can be found in the gall-bladder. 
The fact that Leeuwenhoek did not record any abnormality in the liver of 
the animal from which he obtained the “ egg-like bodies ” does not, therefore, 
weigh against the interpretation here advanced. The recorded findings are, 
on the contrary, quite consistent with my conclusions. 
If the interpretations here advanced are correct, then it must be con¬ 
cluded that Leeuwenhoek discovered and described the oocysts of Eimeria 
stiedae as long ago as 1674. It is true that he did not know what they were: 
but then neither did any of the earliest observers of the Coccidia. The fact 
remains, none the less, that he discovered them: and if this be admitted, then 
it must also be admitted, I think, that these observations are among the first 
ever made upon the Protozoa. It is true that Robert Hooke described and 
figured the shell of a foraminiferan about ten years earlier—calling it a 
“small Shel-fish” (see Hooke (1665), Obs. xi, p. 80, and Scheme V, Fig. x). 
Nummulites—large fossil shells of Foraminifera—were also known to Strabo 
the geographer, and doubtless to others among the ancients: but none of these 
writers can properly be said to have “discovered” the Protozoa. Leeuwen¬ 
hoek’s famous letter describing free-living protozoa in various waters is 
generally allowed to be the first in which the living animals were described. 
It was written in 1676 and partly published in the Philosophical Transactions 
in 1677, but describes a number of discoveries made in 1675. Yet his discovery 
of the oocysts of E. stiedae appears to have been made still earlier, and the 
observations on this organism are, so far as I have been able to ascertain, 
among the first which Leeuwenhoek ever made on Protozoa of any sort. 
Consequently, they are probably—if we except Hooke’s foraminiferan shell— 
the first microscopic observations on the Protozoa 1 , the first on any parasitic 
protozoon 2 , and the first on any species of the Coccidia. 
The conclusions which I draw from the foregoing considerations are, 
therefore, as follows. The Coccidia were discovered by Leeuwenhoek, who 
made a brief but recognizable reference to the oocysts of Eimeria stiedae 
in 1674: but he did not know what thev were, and his observations were 
never published. The first published account of the oocysts of this parasite 
There are, I believe, a few observations on free-living protozoa in a slightly earlier letter 
(Sept. 7, 1674), but these are not generally known, and the letter has not yet been printed in full. 
Leeuwenhoek s observations on Giardia intestinalis —which I have discussed in detail else¬ 
where (Dobell, 1920) are dated 1681; and the better known letter on the ciliates of frogs was 
written in 1683. 
