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.^ 



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

 suffer most from abortion.^ 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 been isolated from outbreaks of abortion in ewes, and has been 

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



Hammond * 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 6'7"4 normal foetuses and 12'4 

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

 In domestic rabbits the proportion of degenerate foetuses was 

 closely similar. Degenerate foetuses iii 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. 



^ Heape, loc. cit. 



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

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

 Agric. Soc, vol. xxi., 1885. 



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

 references. 



