342 THE DISCOVERY OF THE COCCIDIA. BY CLIFFORD DOBELL, F.R.S. STUDENTS of the history of Protozoology are generally agreed that the earliest recorded observations on the Coccidia are those of Hake (1839). Biitschli (1882, p. 490) mentions his work, though he did not see it; and it has been cited by Leuckart (1879), Labbe (1896), and several other writers on the Sporozoa—including myself (1919)—as the first publication in which coccidia are recognizably described1. Dr Thomas Gordon Hake was a practising London physician. His book is now extremely rare, and has probably been seen by but few protozoologists. In this work he described the lesions caused by Eimeria stiedae in the rabbit's liver, and gave an account, accompanied by admirable figures, of the un- segmented oocysts of this parasite. But Hake's description—though it appears to be the first in which any stages of the coccidia themselves were described— is not the first account of coccidial lesions in the rabbit: for I find that in the previous year (1838) Robert Carswell—at that time Professor of Pathological Anatomy at University College, London—published a coloured picture of a rabbit's liver showing the lesions caused by E. stiedae. It is to be found2 in the section devoted to "Tubercle" (last section of the book), on Plate II (illustrating this section), Fig. 6; but the lesions shown in the bile-ducts— which are partly dissected out—are described in the accompanying letterpress as "a beautiful illustration of the seat of tuberculous matter in the liver of the rabbit." The lesions are, however, to my mind clearly those of coccidiosis —not of tuberculosis. In his interpretation of his own findings Hake was no happier than Carswell. For him the coccidial lesions were not tuberculous, but constituted a "carcinoma of the bile-ducts"; while the unripe oocysts which he found in them were described as being "a new form of the pus globule," though they were also called more objectively "ovate corpuscles." Nevertheless, in spite of his errors Hake probably deserves the credit of being the first to 1 Diesing (1851, p. 16) has supposed that sporozoan parasites were seen by Redi in Crustacea: but Biitschli, Leger, and other authoritative writers on the Sporozoa, have rejected this supposi- tion; and after a careful study of the original work of Redi (1684) I consider their conclusions fully justified. At all events, I think there can be no doubt that the things which Redi found in crabs were certainly not coccidia—whatever else they may have been. 2 In Carswell's book the pages are not numbered, nor are the plates numbered consecutively. I trust, however, that the particulars given above will suffice to enable anybody to find the figure in question. The book itself is rare, and not readily accessible. Carswell is mentioned by some of the writers on the Coccidia, but usually without any exact reference to his work. C. DOBBLL 343 describe coccidia, in a recognizable manner, in any printed work. It is not my aim, in the present paper, to dispute his claims in this respect: but I hope to be able to show that another and a greater man discovered the "ovate corpuscles" long before Hake was born; and not only discovered them, but left a record of his observations—a record which was written nearly 250 years ago, but which has never yet, I believe, been read aright, and has certainly never yet been printed. It is well known that the celebrated Dutch microscopist Antony van Leeuwenhoek (1632-1723), the discoverer of the Protozoa, never published his earliest letters—though his real reasons for not doing so are still unknown. In both the Dutch and the Latin printed editions of his collected works the first epistle is that which he himself called his "28th Letter" (April 25, 1679): and a note by the publisher informs us that "the previous 27 letters written by the author, he could not hitherto resolve to make public by printing: and thus the 28th is the first that is here printed1." Yet these early letters are not lost. The original manuscripts, written in Dutch, have been carefully kept2 by the Royal Society, to which body they were addressed: and as they are all dated, it is not difficult, for anybody who will take the trouble, to ascertain their true sequence and the distinguishing numbers which Leeuwen- hoek himself probably assigned to each. Moreover, some of these letters have been partly printed, in the form of English or Latin abstracts, in the early volumes of the Philosophical Transactions: but these are fragmentary and incomplete, and convey a very imperfect idea of the originals; while at least eight have never been printed at all, and their contents have, to the best of my belief, remained entirely unknown to the scientific world from that day to this. During the last few years I have made a careful study of these early un- published letters, and I have found many very interesting observations recorded in them. I hope to be able to say more about these letters on a future occasion; but in the present note I wish to direct special attention to only one of them—a letter (entirely unpublished hitherto) which is dated October 19, 1674, and which is, according to my reckoning, the "7th Letter" in the whole series. It is not very long—not long, that is to say, for Leeuwen- hoek—for it consists of only five large and rather closely written pages. It is addressed to Henry Oldenburg—then Secretary of the Society—and contains a number of microscopic observations on bile, fat, sweat, etc. The observa- tions on bile are in some respects so remarkable that I think no apology is needed for publishing them. As Leeuwenhoek's Dutch would not be readily intelligible to most modern scientific readers, I have—though not without reluctance—translated the passage in question bodily, and as literally as 1 See the Dutch works of Leeuwenhoek, II Deel, ad init. (Register der saaken). 2 I should state that there are three exceptions; for the first letter of all, and two others which I believe to have been the 17th and 27 th, are missing. The first was partly printed, however, in the Philosophical Transactions for 1673. The others are, I believe, wholly and irrecoverably lost. 344 The Discovery of the Coccidia I can, into English. I will now give this translation, and will make my comments upon the observations afterwards1. From Leeuwenhoek's 7th Letter, October 19, 1674. The bile of an ox was examined [i.e. with the microscope] by me on the 1st instant [i.e. 1 Oct. 1674], and therein I beheld some few globules that floated in the liquid; but [I saw them] only when I set the bile in a continual motion before my sight, for it would else have been impossible for me to perceive the globules in it, owing to their fewness in the bile that I was examining. But afterwards, examining the bile of another ox, I found that the globules were of a heavier matter than the liquid that they floated in; wherefore I drew off the bile from the bottom of the gall-bladder, and then found that there were many hundred times more globules in this bile than in that which I ha,d taken from the upper part of the gall-bladder; and there were, besides, some corpuscles which, to my eye, looked as big as ants' eggs2. These had the figure of an egg [i.e. a hen's egg], only with this differ- ence, that whereas an egg is more sharply pointed at one end than at the other, yet these corpuscles were equally pointed at both their ends: and moreover these corpuscles were composed of globules joined together, and had a yellow colour, except several which were somewhat whitish; but notwithstanding, they were so transparent that you could see the body of one through that of another. And this transparency making me wonder whether they were not, in fact, little vesicles filled inside with liquid, I took some of these corpuscles out of the bile with a fine hair; and examining them on the hair, I perceived two which seemed tp be bent in, just as though you had filled a bladder with air and then put your thumb on it, so as to make a dent in it: whereupon I was the more firmly persuaded that these corpuscles were filled with some sort of liquid. Afterwards, examining more biles from oxen, I found them the same as before; only with this difference, that one bile would contain more of the oval corpuscles than another. In the bile of two calves I find, furthermore, some very little globules floating, and very many irregular particles of divers forms; among others, some like little floating clouds, all consisting of very little globules joined together. On seeing these irregular aggregated particles, I judged them to be joined or stuck together through no other cause than because the bile had got cold, and was without motion. In the bile of a third calf there were a few oval corpuscles. Moreover, in the bile of sucking lambs I find there are very little globules, and some, though very few, bright particles, which are a bit bigger; besides irregular particles, of divers figures, and also composed of aggregated globules. The bile of a yearling sheep I find to be like that of sucking lambs, only with this difference, that in this bile there are also oval corpuscles of the bigness and figure of those that I remarked in ox-bile.