FERTILITY 143 



being present in the cock only, and transmitted by him to the 

 next generation of hens. With man, Pearson has found that 

 fertility is inherited equally through the male and female lines. 



Artificial Insemination 



An account of all the anatomical and other conditions which 

 cause sterility is outside the scope of this book. Attention 

 may, however, be drawn to those individual peculiarities which 

 may be overcome by resorting to artificial insemination — that 

 is, the injection of semen into the female passages at the 

 season of oestrus or about the time when ovulation is beheved 

 to occur. 



Artificial insemination in a mammal was probably first 

 demonstrated in the eighteenth century by the Italian naturalist, 

 the Abbe Spallanzani, though there is evidence that it was not 

 unknown to the Arabs in very much earlier times (Heape). 

 Spallanzani succeeded in impregnating a bitch spaniel in this 

 w^ay by injecting semen, obtained from a dog by spontaneous 

 emission, into the vagina of the bitch, which in due time gave birth 

 to a litter of pups. Since SpaDanzani's time artificial insemina- 

 tion has been practised successfully upon mares, cows, and other 

 animals, and usually with a view to curing sterility. It has also 

 been performed when it was desired to get crosses between animals 

 sho\ving great disparity in size (making normal coition difficult), 

 as in Millais' experiments in which bloodhounds were inseminated 

 with spermatozoa obtained from Basset hounds (a much smaller 

 breed). Moreover, Ivaiioff has recorded an experiment in which 

 he inseminated a mouse with the sperm of a rat and obtained 

 two hybrid young ones. 



Artificial insemination as a means of overcoming certain forms 

 of sterility in women has been performed by various medical men 

 from the time of Hunter in the eighteenth century. The method 

 adopted is to inject the semen directly into the uterus through 

 the OS, by means of a syringe, the fluid in most cases being 

 obtained from the vagina of the same individual. In this way 

 it has been found possible to overcome such structural defects 

 as constriction or undue rigidity of the os uteri, or hypertrophy 

 of the lips of the external os. By modifying the method by which 

 the semen is obtained it has proved possible to induce pregnancy 



