362 THE PHYSIOLOGY OF I^EPRODUCTION 



recurrence of heat and menstruation.^ It has been observed that 

 not only are the uiternal and external generative organs affected at 

 these periods, but there is also a distinct hypertrophy of the breasts, 

 and this, as Miss Lane-Claypon and Starling ^ have pointed out, is 

 probably due also to an increase in the ovarian metabolism.* 



There is a certain amount of direct evidence that heat and 

 menstruation are brought about by an internal secretion elaborated 

 by the ovaries. It has been found that the injection of fresh ovarian 

 extract obtained from animals which are " on heat " may appear to 

 produce in ancestrous animals a transient congestion of the external 

 generative organs resembUng that of the normal prooestrous condition, 

 but similar slight indications have been observed at other times 

 irrespectively of any injections.* Miss Lane-Claypon and Starling 

 also have described congestion in the uterus after the injection of 

 ovarian extract; but, in their experiments, the ovaries employed 

 were those of pregnant animals. Moreover, Aschner ^ has described 

 uterine haemorrhage after injection of ovarian extracts. 



Further evidence that the prooestrous and oestrous conditions are 

 produced by substances circulating in the blood, but not necessarily 

 elaborated in the ovaries, is supplied by certain facts recorded by 

 Halban.^ This author affirms that the milk of suckling sows is 

 affected during the periods of heat, in consequence of which the 

 young are hable to develop unhealthy symptoms. In a similar way 

 the milk of women is said to be affected during menstruation. 

 Moreover, according to Youatt,'^ cows can be brought "on heat" 

 artificially by feeding them on milk supplied from other cows which 

 are in that condition. 



^ As already pointed out, menstruation and ovulation are not necessarily 

 associated. It is probable, however, that the ovarian metabolism is increased 

 at the menstrual periods, although there may not always be any follicles present 

 in a sufficiently mature condition to admit of ovulation occurring in the 

 oestrous periods which normally follow them. 



^ Lane-Claypon and Starling, "An Experimental Inquiry into the Factors 

 which Determine the Growth and Activity of the Mammary Glands," Proc. 

 Roy. Soc, B., vol. Ixxvii., 1906. 



^ According to Pearl and Surface ("The Nature of the Stimulus which 

 causes a Shell to be formed on a Bird's Egg," Science, New Series, vol. xxix., 

 1909), the stimulus which excites the activity of the shell-secreting glands in 

 the fowl's oviduct is mechanical, being brought about by a strictly local reflex. 

 The shape of the egg is determined by the muscular activity of the cells of 

 the oviduct (Pearl, " Studies on the Physiology of Beproduction in the Domestic 

 Fowl : I. Regulation in the Morphogenetic Activity of the Oviduct," Joim: 

 of Exp. Zool., vol. vi., 1909). 



* Marshall and Jolly, loc. eit. 



■> Aschner, "Ueber brunstartige Erscheinungen (Hyperamia und Hamor- 

 rhagia am weiblichen Genitale) nach subkutaner Injektion von Ovarial- und 

 Plazentaextrakt," Arch.f. Oynak., vol. xcix., 1913. Cf. Iscovesco, C. R. de Soc. de 

 Biol., vol. Ixxiii., 1912. 



" Halban, ^oc. dt. 



• Youatt, Cattle, London, 1835. 



