THE FARMER'S MAGAZINE. 



338 



iiig its way in juat below the skiu by the cilia which it pcs- 

 geaaea, it undergoea a perfect change, bccomiug aoiuethiug like 

 a chryaalis, iu which conditiou it propagates itself ; that the 

 creatures immediately coming from it reach a certain order of 

 development in the snail ; that they then escape from it, swim 

 about iu water, and, after a certain time, again become en- 

 cased, and again become parasitic to the anail, in order, in 

 reality, that they may reach a higher form of development. 

 This is explained in one of my diagrams. Putting aside the 

 eias as representative of the distoma, we go back to a peculiar 

 organism, as an analogy, which is often met with in small 

 water snails, slugs, and the like, imbedded underneath the 

 common integument in different parts of the body. It has 

 been called a cercaria-sac, so called from the creature which 

 issues from it being a creature with a tail, which swims about 

 in water. la this sac we have vital germs —very small 

 granular matter — which are sent off as gemma; or buds, lying 

 beside a kind of intestinal canal. We find this budding pro- 

 cess goi s on, and we have a considerable number of these germs 

 ultimately set at liberty ; within the sac these develop into the 

 true cercaria, and when they have arrived at a certain period 

 of development they burst through the sac, and swim freely 

 about in water. The diagram represents the different degrees 

 of development. You have first the small germ, which as a 

 gemma or bud, comes off, becomes elongated in one part of its 

 body ; that subsequently elongates into a tail-like appendage, 

 other organs are then added, and in this condition the creature 

 bursts through the sac, leaving others to come out of it pro- 

 duced in the same manner. It swiraa about in water with a 

 long floating tail, and it has been viewed as one of the infusoria. 

 Subsequently it curia itself up, and as a general rule gets in the 

 first instance upon slugs, entering the slimy matter which 

 covera them, and imbeding itself in that. It then becomes 

 encased in a kind of shell again, and lies just underneath the 

 akin of the snail, and from this state it goes on developing 

 within the snail until it forms a distoma. So that there is no 

 doubt, whatever may be the origin of these cercaria, so far as 

 they are parasitic to anaih, we have traced the whole history of 

 them. Therefore by analogy we i-nagine that, as we h;ive 

 germs of a similar nature which become parasitic from the 

 ova of the true liver ilukc, that these pass through a series of 

 similar changes, and that iu this imbedded condition they 

 either remain in the water attached to plants, or to smaller 

 creatures inhabiting water, especially slugs and snails ; and 

 that when these pass iuto the stomach of the sheep they 

 find their proper Jiabitat, and develope into flukes. It 

 is important to bear in mind that the last transforma- 

 tion takes place, nor in the liver, not in the biliary ducts, 

 but in the stomach or intestines ot the animal. You will see 

 presently what importance there is attaching to this fact, 

 which has only very recently come to light. Now, 

 if we accept this as au approximation to the trulh with 

 regard to the development of flukes, we shall find that 

 it unravels the whole mystery with reference to rot. It 

 explains at once why certain districts are dangerous. It 

 explains the occurrence which has been recorded over 

 and over aj^ain, that out of a hundrel sheep, for example, 

 ninety-iiiue having strayed over a common, and one having 

 been accidentally prevented from doing ao; that subsequently 

 the ninety-nine have been attacked with rot, while the one 

 that remained behind escaped, I have recently received a 

 letter from a well-known agriculturist — Mr, Edward Umbers, 

 of Wappenbury— in which he has been kind enough to give 

 me the particulars of two cases of this kind. Many years 

 ago some sheep belonging to his father were found, subse- 

 quently to their purchase, to be affected with rot, and in 

 tracing the matter out it was found that the sheep had been 

 left in what was called a dangerous part of the country for a 

 short space of time while the man went into a public-house 

 close by to get some refreshment. If you look at Mr. 

 Youatt's work you will see numerous cases of this descrip- 

 tion. And what is the explanation of them ? I have known 

 the time when I have stood in the lecture-room of our own 

 Institution and combatted this view, and never could 

 become a convert to it till I became more enlightened 

 as to the natural history of these entozoa. I now 

 believe that it is perfectly possible for sheep to be free 

 from the cause of rot at this minute, and to receive it at the 

 next ; that is, if they are placed under circumstances where 

 they can obtain these creatures in one of their forms, or in a 



particular stage of development. Now let us suppose we 

 have the cercaria rolled up into the form of a creature some- 

 thing like a chryaalis covered over by its shell; let us also 

 suppose that which is positively the fact, that hundreds of 

 these creatures can be seen upon small molluscs, many of 

 them also loose in water — that they are adhering like- 

 wise to plants and growing in damp situations ; then a 

 sheep has only to drink a mouthful of water to take iu 

 an infinite number of these creatures, and, taking them into 

 tbestoraach,they there become developed into flukes. We have 

 therefore, very good ground for believing tliat rot can be very 

 readily and rapidly received. Now there are certain difficult 

 ties which people put before us with regard to this theory. 

 They want to know how it is that we get rot in certain sea- 

 sons and not iu others. Well, we show that whenever there 

 is an excess of moisture — whenever, in fact, we have great 

 rain-falls — certain pastures and place, which are perfectly 

 free from the disease at other times, now become affected. 

 This ii easily enough explained. We have seen that the ova 

 of these creatures come out in millions from one affected 

 sheep : what, then, must be the number of them in hundreds 

 of sheep so affected ! Now, by direct experiment, I have 

 proved Ibis — that you may take the ova of these fluke?, and 

 keep them upwards of a year bcfori there is any change taking 

 place in them. We know not, therefore, what is the duration 

 of the life of these ova. It is just possible that they may re- 

 main, not only one year, but two years, without undergoing 

 change, until placed under favourable circumstances to under- 

 go that change. If, then, we look at the vast numbers in 

 which these ova exist, and at their power of maiataining their 

 vitality for a great length of time, we get rid of a considerable 

 amount of difficulty. Then we find that when we have au 

 excess of moisture, and with that an elevated temperature, 

 the living germs, if I may sd call them, that are now 

 separated by the bursting of the operculum of the egg, are 

 set at liberty and become parasitic to other creatures, 

 passing through the series of transformations comparatively 

 quickly, and being at length very easily received into the 

 system of the sheep. I have referred to an elevated tem- 

 perature combined with excessive moisture; and what is the 

 practical observation which is made with reference, for in- 

 stance, to watery meadows ? It is notorious that sheep placed 

 upon water meadows receive the rot ; but it is equally 

 notorious that it is only at a certain period of the j-ear that 

 they will dj so. You may, as every practical man knows, put 

 sheep upon water-meadows during the winter months, or in 

 the early part of the spring ; but if you water your meadows 

 in the mouth of May, and then get a luxuriant herbage 

 springing up afterwards, and put the sheep on this, you are 

 almost certain to rot them. As you approach Midsummer, 

 the danger increases; and as you approach the winter, it 

 decreases. That single circumstance shows that, when there 

 is moisture and heat combined, the cause of rot is brought 

 into operation. I have spoken of the great losses amongst 

 sheep affected with the disease. When were the sheep first 

 affected with rot that we are now losing? I answer, last Mid- 

 summer and forwards towards the autumu. That ij the time 

 to which you have to look. The cause was received then; 

 the development has been going on in the flukes since 

 that time. They have now attained their full size, and 

 they are producing mischief in anoemiating the sheep. 

 When we talk about curing rot, we must talk about 

 taking cognizance, if poasible, of the early existence of 

 the disease ; then is the time to bring into operation cer- 

 tain causes which will prevent the malady. I have here, 

 for the inspection of the members, some early-developed flukes, 

 the only early ones I have been able to meet with. I have 

 had them by me seven or eight years. They were taken out 

 of a young sheep — and this is an exceedingly interesting fact, 

 because it bears out what I have said — in which there waj not 

 one large fluke, and consequently there was not a single ovum 

 in the duds. They are simply the youngest form of the fluke 

 development from out of the infusorial creatures to which I 

 have before referred, that have found their way into the biliary 

 ducts. They were sent me by an amateur pupil of the Vete- 

 rinary College, from Redgrave, in Suffolk. They were taken 

 by him, in September, 1853, from some lambs which had 

 come on the farm six weeks before. It was a marshy farm, 

 and the lambs were placed literally upon fen-land, as it is 

 called. Having explained, though not ao much at length as I 



