656 THE PHYSIOLOGY OF REPRODUCTION 



percentage of abortion. "Sheep-stained " pasture (i.e. pasture grown 

 with the aid of sheep manure or on which sheep have been run for 

 a considerable time previously) is credited with causing abortion, and 

 there is strong evidence in support of this view in cases where rank 

 or over-stimulated growth results. 1 



As already noted, the Dorset Horn and Lincoln breeds of sheep 

 suffer most from abortion. 2 In the case of the former this may result 

 partly from in-breeding, since Dorset Horn ewes served by Hampshire 

 Down rams are less liable to "slip lamb" than those served by rams 

 of their own breed. It is possible, therefore, that the abortion may be 

 due to a want of vitality on the part of the developing embryo, the 

 cross-bred young possessing a superior vigour. Abortion among 

 Lincoln sheep has been known to reach thirty, forty, or even fifty 

 per cent., and so to assume an epidemic form. Wortley Axe, :{ who 

 reported on an outbreak of abortion among the Lincolnshire flocks in 

 the season of 1882-83, was disposed to attribute it to debility, arising 

 largely from foot-rot and exposure to cold winds and heavy continuous 

 rains, as well as to the feeding of the ewes on unripe, watery roots 

 and unwholesome, filth-laden shells. Heape has suggested that 

 abortion on the Wolds arises partly from the practice of unduly 

 crowding the ewes on turnip fields. As already mentioned, a bacillus 

 has l)een isolated from outbreaks of abortion in ewes, and has been 

 used to infect other ewes for experimental purposes in the laboratory. 



Hammond 4 has shown that atrophy of foetuses in utero is a very 

 common phenomenon in pigs as well as in domestic rabbits. It occurs 

 at different degrees of embryonic development, and degenerate 

 foetuses of different sizes and in a mummified condition are commonly 

 found in the same uterus. Hammond counted the foetuses in the 

 uteri of twenty-two sows and found that for 100 eggs shed (shown 

 by the corpora lutea) there were 67'4 normal foatuses and 12'4 

 atrophic foetuses (leaving 20'2 ova missing or unaccounted for). 

 In domestic rabbits the proportion of degenerate fcetuses was 

 closely similar. Degenerate foetuses in utero have been recorded 

 also for the following animals : mare, cow, sheep, goat, guinea-pig, 

 hamster, rat, mouse, ferret, dog, cat, and mole. The proportion of 

 atrophic foetuses in wild rabbits is very much smaller than in tame 

 ones, and Hammond draws the conclusion that the fertility of many 



1 Abortion in sheep may result from more exceptional causes. Thus it is 

 recorded that a large proportion of a certain flock of Cheviot ewes slipped lamb 

 after a gale which blew down a number of Scotch fir trees, the abortion resulting, 

 in the owner's opinion, from the animals eating the branches and bark. See 

 Marshall, loc. cit. 



2 Heape, lo<: , //. 



3 Wortley Axe, "Outbreak of Abortion and Premature Birth in the Ewe 

 Flocks of Lincolnshire during the Winter and Spring of 1882-83," Jour. Royal 

 Agric. SW., vol. xxi., 1885. 



4 Hammond, loc. cit., 1913 and 1921. These papers contain further 

 references. 



