616 THE PHYSIOLOGY OF REPRODUCTION 



of danger at the end of the third and sixth weeks, but that the 

 most critical period is about the end of the seventh or beginning 

 of the eighth week ; for unless the villi appear in time, and 

 succeed in coming into sufficiently intimate relation with the 

 uterine vessels, the developmental process is of necessity for 

 ever arrested." 1 



Ewart discusses briefly the external conditions and circum- 

 stances which are likely to lead to abortion, and provides some 

 useful practical hints as to the best way to treat mares in order 

 to prevent them from " slipping foal." He remarks that the 

 horse is a peculiarly high-strung^ nervous animal, and is easily 

 affected by sudden changes in its surroundings, especially during 

 the breeding season. Such changes are, no doubt, often re- 

 sponsible for setting up disturbances in the nervous system, 

 and so inducing abortion, more particularly at that period of 

 development at which the fixation of the embryo to the uterine 

 wall is relatively insecure. 



Abortion in cows is said to be commonest during the first 

 month of pregnancy. According to Wallace 2 the usual causes 

 are the following : (1) Eating ergotised grass ; (2) injury due 

 to horning by other cattle, hunting by dogs, or shaking and 

 bruising in travelling, &c. ; (3) physical strain, resulting from 

 walking over too soft land, &e. ; (4) very cold or foul water, 

 or frozen turnips, &c. ; (5) superpurgation, whether occurring 

 naturally or as a consequence of dosing by physic ; (6) contagion 

 from other cows affected by epidemic abortion. This is said to 

 be the commonest and at the same time the most dangerous 

 cause of abortion. 



Bang 3 has shown that contagious, epidemic, or epizootic 

 abortion in cattle is due to a specific bacillus which he has been 

 able to isolate and cultivate in oxygenated glycerine-bouillon 

 or serum-gelatine agar. The germ causes the formation of a 

 brownish-yellow exudate between the chorion and the mucous 



1 Ewart, loc. cit. 



2 Wallace (K.), loc. cit. Wallace states that after abortion in cattle the 

 placenta adheres to the cotyledons, and should be removed artificially ; 

 otherwise it is liable to undergo a process of rotting, sometimes resulting 

 in septicaemia and death. 



3 Bang (B.), " Infectious Abortion in Cattle," Nat. Vet. Soc., Liverpool, 

 July 25, 1906. 



