760 HANDBOOK OF PHYSIOLOGY. 



forming a true decidua menstrualis (fig. 454), while Moricke and others 

 believe that the mucous membrane remains intact. Leopold believes 

 that red blood corpuscles escape from the congested capillaries and un- 

 dermine the superficial epithelium, and that in this way the superficial 

 layer of the mucous membrane is eroded and subsequently regenerated. 

 It is probable that menstruation is not a sign of the capability of being- 

 impregnated, as much as of disappointed impregnation. 



Menstrual Life. The occurrence of a menstrual discharge is one of 

 the most prominent indications of the commencement of puberty in the 

 female sex ; though its absence even for several years is not necessarily 

 attended with arrest of the other characters of this period of life, or 

 with inaptness for sexual union, or incapability of impregnation. The 

 average time of its first appearance in females of this country and others 

 of about the same latitude, is from fourteen to fifteen ; but it is much 

 influenced by the kind of life to which girls are subjected, being accel- 

 erated by hatits of luxury and indolence, and retarded by contrary 

 conditions. Its appearance may be slightly earlier in persons dwelling 

 in warm climes than in those inhabiting colder latitudes. Much of the 

 influence attributed to climate appears due to the custom prevalent in 

 many hot countries, as in Hindostan, of giving girls in marriage at a 

 very early age, and inducing sexual excitement previous to the proper 

 menstrual time. The menstrual functions continue through the whole 

 fruitful period of a woman's life and usually cease between the forty- 

 fifth and fiftieth years. 



The several menstrual periods usually occur at intervals of a lunar 

 month, the duration of each being from three to six days. In some 

 women the intervals are so short as three weeks or even less; while in 

 others they are longer than a month. The periodical return is usually 

 attended by pain in the loins, a sense of fatigue in the lower limbs, and 

 other symptoms, which are different in different individuals. Menstru- 

 ation does not usually occur in pregnant women, or in those who are 

 suckling; but instances of its occurrence in both these conditions are by 

 no means rare. 



Corpus Luteum. Immediately before, as well as subsequent to, the 

 rupture of a Graafian follicle, and the escape of its ovum, certain changes 

 ensue in the interior of the vesicle, which result in the production of a 

 yellowish mass, termed a Corpus luteum. 



When fully formed the corpus luteum of mammiferous animals is a 

 roundish solid body, of a yellowish or orange color, and composed of a 

 number of lobules, which surround, sometimes a small cavity, but more 

 frequently a small stelliform mass of white substance, from which deli- 

 cate processes pass as septa between the several lobules. Very often, in 

 the cow and sheep, there is no white substance in the centre; and the 



