C. Dobell 
165 
sultation of the literature on this subject will show that, in each of these 
respects, the view which any writer takes of the coccidia of man depends very 
largely upon the opinions which he holds concerning the coccidia parasitic in 
rabbits, and those of dogs, cats, and other carnivores. Until recently there 
has been much uncertainty about these parasites; and it will greatly facilitate 
the comprehension of what I have to say in the ensuing paragraphs if the 
present state of our knowledge of them is made clear at the outset. I shall 
therefore devote a short space to the consideration of this subject before pro¬ 
ceeding further. 
The coccidia of the rabbit. As is generally known, the common rabbit, both 
wild and domesticated, usuallv harbours coccidia in its liver and small intes- 
tine. In the liver they infest the bile canal system, in the gut the epithelium 
> 
of the mucous membrane; and in both situations they may give rise to patho¬ 
logical conditions of variable and sometimes fatal extent. 
The coccidia of the liver were discovered, by T. G. Hake, a London physician, 
in 1839 1 . He did not, however, understand their true nature; but regarded the 
lesions in the liver as “carcinoma,” and the parasites as “a new form of the 
pus globule.'' As a result, however, of the labours of many later workers in 
several different countries—it will suffice to mention Remak, Kolliker, Stieda, 
Lieberklihn, Rivolta, Leuckart, and Balbiani—the parasites gradually came 
to be regarded in their proper light; so that by about 1880 they were generally 
recognized as protozoa belonging to the group of “oviform psorosperms" or 
Coccidia. Hake (1839) had already found oocysts in the contents of the 
duodenum, and later Klebs (1859) demonstrated the parasites within the 
epithelial cells of its mucous membrane. Since then there has been a prolonged 
controversy over these parasites, and even now it cannot be regarded as 
finally decided. The majority of modern workers follow Balbiani (1884) in 
regarding the coccidia found in the liver and the intestine as belonging to the 
same species—the site in the host’s tissues being their sole distinctive character. 
Others, adopting the standpoint of Leuckart (1879), regard the parasites of the 
intestine as specifically different from those in the liver, and advance various 
reasons in support of their belief. To my mind, the evidence at present avail¬ 
able, both morphological and experimental 2 , is undoubtedly in favour of the 
1 It may be noted that Hake’s work contains the earliest account and figures of coccidia known. 
His drawings of the oocysts from the liver are admirable, and might serve as illustrations for a 
modern text-book. 
2 The most important experimental evidence is that adduced by Railliet and Lucet (181)1), 
Railliet (1895), and Lucet (1913). According to these workers the spores of the hepatic parasite, 
when ingested, produce a hepatic infection only: and similarly, those of the intestinal parasite 
produce an intestinal infection only. If the work of Lucet (1913) is sound, as there appears no 
reason to doubt, then it seems certain that his conclusions are correct—namely, that there are two 
distinct species in the rabbit. So far as my own observations enable me to judge, the morphological 
differences which he describes between these species actually exist, and at present I agree with his 
conclusions. Moreover, I can find no adequate arguments against his views in the work of Metzner 
(1903), Reich (1913), and others who hold an opposite opinion. 
