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THE FARMER'S MAGAZINE. 



tion of generations, but to show besides that traces of a 

 similar development are visible in almost all the divisions 

 of the class. According to recent observations it is, how- 

 ever, exhibited most clearly in the trcmatoda [the order to 

 which the fluke belongs], in which I prove that cercarioi 

 are the larva of distomata, and that they become true 

 2)upce ; that the animals in which the cercariw originate, 

 and grow up are trematode individuals descended in the 

 second or third generations from distomata, and conse- 

 quently not produced from their ova, but which, however 

 anomalous they may at first sight appear, constitute a pre- 

 cedent generation having for its object the perfecting of 

 the subsequent one." 



In other words, whUe animals lUie the horse and cow 

 produce young which are miniature copies of themselves, 

 the process of reproduction in various classes of entozoa 

 is so conducted that whilst, until the ofi'spring has 

 undergone several forms of gradations of being, each 

 succeeding one dissimilar to those which preceded it, it 

 docs not attain to the "dignity" of the parent stock, ye/, 

 in several of these gradations, the larva as it approaches 

 maturity has the power of developing a number of creatures 

 resembling itself, just as though, to use the language of 

 Dr. Lankester, " the caterpillar had the power of produc- 

 ing in its interior any number of young caterpillars, each 

 of which would gi-ow into a ^perfect butterfly." This 

 may seem a very round-about way for nature to work in, 

 but it at once explains the difficulty that has hitherto 

 attended every effort of English observers to detect the 

 precise form in which the larvas of the fluke find their 

 way into the gall duets of the sheep, there to undergo their 

 final stage of development. The theory is, at all events, 

 more rational than that of equivocal generation, in which 

 scientific men of a by-gone era were content to enshroud 

 their imperfect knowledge, and we shall very inadequately 

 perform oiu- duty if we shrink from the wide field of in- 

 vestigation which is thus opened up. 



According to Gerlach, as quoted by Kiichenmeister in 

 his " Manual of Parasites"* (vol. i. p. 2G8), the eggs of the 

 liver fluke (disloma hepaticum) have been administered to 

 ambs without producing any ill effects upon them. From 

 this circumstance, in conjunction with the theory of Stecn- 

 strup, it is argued that the body of the sheep does not 

 afford a congenial nidus for the hatching of the ova, and 

 that the ova, after leaving the body of the sheep, must 

 l^ass through one or two gradations of development before 

 the organism of the sheep is favourable to their matura- 

 tion. Siebold, in his treatise " On the Origin of Intestinal 

 Woi-ms " — another of the authorities for the knowledge of 

 which the English public are indebted to the labours of 

 the Sydenham Society— says (p. 4) : "It has been ascer- 

 tained that at particular periods of then- existence, the 

 intestinal worms undertake emigrations, and these often 

 very extensive ones, in order to reach that animal whose 

 organs are by nature fitted for their habitation," and after 

 illustrating his position by a reference to the reproduction 

 of tape-worms, he observes that " the same thing holds 

 good with regard to the ova of the dismotata that infest the 

 livers of our ruminating animals ; their eggs, after they 

 have been transferred from the liver to the gall-ducts, being 

 washed out with the bile into the intestine and evacuated 

 with the ffeees." But what becomes of the ova after their 

 liberation from the body of the sheep, and in wliat form or 

 stage of development do they find their way back to it ? 



* Traaslated by Dr. Lankester, and jjuWisbcd by the Sydeii- 

 liani Society, 1855. 



Here we confess that the researches of German heluiin. 

 thologists fail to give us that precise and positive informa- 

 tion which alone can be regarded as conclusive or satis- 

 factory. Steenstrup, it is true, as stated in an early part 

 of this article, gives the result of his observations up to 

 the point which is most critical and important, but there 

 he stops; and though we agree with Kiichenmeister (vol. 

 i., p, 268), that after 1855 " it was not difiScult to conjec- 

 ture that sheep, rabbits, men, &c., might infect themselves 

 by devoiuing small mollusca inhabited by the brood of the 

 distoma in question, which were living upon the grass of 

 the meadows, or by swallowing small aquatic mollusca, or 

 free broods of distoma, when drinking from stagnant, 

 marshy waters," yet this, after all, apart from the scientific 

 phraseology in whicli it is couched, carries us very little 

 farther than the observations of a practical agriculturist, 

 who, in the second volume of the Bath Society's papers 

 (a.d. 1783), remarks as follows : 



" They (the flukes) are swallowed with the sheep's food 

 while in the egg state. The common or most obvious ob- 

 jection to that opinion is, that this insect is never found 

 but in tlie liver or some parts of tlie viscera of sheep that 

 are diseased more or less ; and that they must, therefore, 

 be bred there. But this objection will lose its force when 

 we consider that many insects undergo several changes, 

 and exist under forms extremely difl'erent from each other. 

 Some of them may, therefore, appear, and Ije well known imder 

 one shape, and not be known to he the same under a second or 

 third. The fluke may be the last state of some aquatic animal, 

 which we at present very ivell know under one or other of its 

 previous forms. If this be admitted, it is easy to conceive 

 that sheep may, on wet ground especially, take multitudes 

 of these ova or eggs in with their food ; and that the 

 stomach and viscera of the sheep being a proper nidus for 

 them, they of course hatch, and appearing in their fluke 

 or last state, feed on the liver of the animal and occasion 

 the disorder. On killing a sheep lately, which was seem- 

 ingly in good health, I examined the viscera carefully, and 

 in some of the passages leading to the liver, which ap- 

 peared turgid, I found a whitish thick liquor, which ap- 

 peared to be all in motion. On applying a pocket-glass, I 

 found it to contain thousands of these flukes, which were 

 apparently just hatched [developed], and about the size of 

 mites. These, if the sheep had not been killed, would pro- 

 bably have soon attained their usual size, and produced its 

 destruction. I am, therefore, of opinion, that if experi- 

 ments were made by some of the faculty to discover what 

 would most speedily Idll these insects when taken fresh 

 and alive from a diseased liver, it might lead to the dis- 

 covery of something that might hare the same efi'ect when 

 given internally as a medicine. We find worms can be 

 destroyed in the bodies of animals, and why not the fluke 

 in the liver of the sheep?" 



We cannot say whether Lord Berners had this article in 

 view when he complained that " the veterinary art is stUl 

 in its infancy ;" but certainly, after surrendering ourselves 

 to a very patient investigation of the writings of Steen. 

 strup, Kiichenmeister, and Siebold, we are more than ever 

 constrained to admit that though our present observations 

 may be more accurate and precise, yet for all practical 

 purposes we know little more of sheep-rot than wo did 

 eighty years ago. Even Sir Anthony Eitzherbert in his 

 "Roke of Husbandry" (a second edition of which was 

 printed in lu^'.O), says, " white snails bo ill for sheep in 

 pastures and in fallows," and though a vast amount of 



