240 



THE ANIMAL PARASITES OF MAN 



spring, but the liver remains changed and its sale is prohibited 1 when 

 the changes are extensive. 2 



[The following stages may be noticed in sheep suffering from 

 fascioliasis. Gerlach recognized four stages, based on the varied 

 relations that the flukes contract with the liver of their host. These 

 periods are sometimes very marked, but at others, owing to subsequent 

 infections, the features become merged and so obliterated. But 

 when a single infestation occurs they are very marked. 



[The first period is called the 



PERIOD OF IMMIGRATION. This 



occurs at the fall of the year and 

 generally passes unperceived, as 

 the young flukes do little harm 

 to the liver. It varies from four 

 to thirteen weeks. Gerlach has 

 remarked upon cases of death 

 from apoplexy at this period. 

 [The second period is the 



PERIOD OF ANEMIA. This OCCUl'S 



in November and December. 

 The sheep at first fatten rapidly, 

 but later the mucous membranes 

 become pale and of a yellowish 



FIG. 142. Fasciolahepatica: egg from liver 

 of sheep, o, operculum, <?, segmenting ovum. 

 The rest of the space is occupied by yolk cells, 

 the granules in three only being shown, x 68c. 

 (After Thomas.) 



FIG. 143. LimntEus tntncatulus, Mull., 

 the intermediate host of Fasciola hepatica. 

 a.f natural size ; b., magnified. (From 

 Leuckart.) 



hue, and the sheep become sluggish and cease to feed. The faeces 

 are normal, but may contain fluke ova. 



[The third period is the PERIOD OF WASTING. This corresponds 

 with the beginning of January about three months after the 



1 [This is not the case in Great Britain ; flaky sheep are sent to market, there being no 

 danger to man from eating the flesh. F. V. T.] 



2 As an example, this occurred in Berlin in the case of 19,034 oxen, 15,542 sheep, 1,704 

 pigs, and 160 calves in the period of 1883-1893 ; during which time 719,157 oxen, 1,519,003 

 sheep, 2,258,110 pigs, and 567,964 calves were slaughtered. As a matter of fact, however, 

 the number of infected beasts was really larger. 



