378 EXAMPLES OF CHEMICAL CORRELATION 



and mammals. However this may be, a considerable storage of cal- 

 cium occurs in the tissues of the female prior to menstruation, and this 

 excess of calcium is suddenly discharged during the period of menstrua- 

 tion. Having regard to the immense importance of the precise value 

 of the ^ ratio in determining the susceptibility of nervous tissues to 

 stimuli, it appears not unlikely that some of the nervous accompani- 

 ments of menstruation, and particulirly the hyperirritability of the 

 uterus which leads to the phenomenon of painful menstruation or 

 Dysmenorrhea may be attributable in part to the sudden reduction of 

 the calcium-content of the tissues which occurs at this period. 



The menstrual blood usually does not clot at all, or if it clots it does 

 so very slowly. This remains the case even if fibrinogen be added to 

 it, and, as .we have seen, calcium is not lacking. It can hardly be 

 deficient in kephalin, or thrombokinase, since the fluid contains so 

 much material arising from the breaking down of the tissues lining the 

 cavity of the uterus. It appears likely, therefore, that the mucous 

 secretions of the uterus contain a substance similar to Antithrombin or 

 hirudin in its action upon the coagulation of blood. 



When the fertilized egg becomes imbedded in the wall of the uterus a 

 proliferation of the uterine wall results in the outgrowth of a Placenta 

 which subsequently provides the developing embryo with circulating 

 blood derived from the mother. We have here a remarkably exact 

 coincidence of events and we are led to inquire why the tissues of the 

 uterus are aroused to the production of this outgrowth at the very 

 moment when it is about to be required? 



An answer to this question has been afforded by the very important 

 discoveries of L. Loeb. This observer has found that in the female 

 guinea-pig, for a period of some ten days following the phenomenon of 

 Ovulation, any injury to the uterine wall results in the outgrowth of a 

 placenta. The injury may be of the nature of a slight incision, in 

 which case a localized growth occurs which may be duplicated at other 

 points in the uterus, so that as many as twenty different placentae may 

 be formed in this way in a single uterus. Or the injury may consist of 

 the irritation afforded by the presence of a foreign object, such as a 

 thin glass rod or a number of particles of paraffin. In this case the 

 growth of placental tissue may become so great as to interfere with the 

 nutrition of the newly formed tissue and induce its degeneration and 

 autolysis. The formation of placentae is prevented if the ovaries are 

 extirpated or even if the Corpora Lutea which they contain are excised. 

 The stimulus which arouses this reaction of the uterus to mechanical 

 irritation comes, therefore, from the corpora lutea. If the corpora lutea 

 are not excised at once, and placentse are permitted to form, they attain 

 a smaller size and degenerate more rapidly if the ovaries or the corpora 

 lutea are excised before their full development is attained. 



Among the many correlations which underlie and render possible 

 the development of the embryo, the next into which we have attained 

 some measure of insight is that which obtains between the development 



