REPRODUCTION AND GROWTH 



When the ovum has been fertilized, it becomes attached to the mucous 

 membrane of the uterus already prepared for it, and later becomes surrounded 

 by the proliferating epithelium of the mucous membrane. 



The material necessary for the nourishment of the ovum is received from 

 the mother through the placenta. As the ovum grows the uterus increases 

 in size, so that while before impregnation its capacity is 3-5 cc., at the close 

 of pregnancy it is 5,000-7,000 cc. This colossal development produces re- 

 markably little change in the organism as a whole, and the only permanent 

 alterations remaining after pregnancy are certain folds in the subcutaneous 

 connective tissue of the abdomen caused by the extreme tension to which it 

 has been subjected, and certain anatomical differences in the wall of the uterus. 



The period of gestation covers ten menstrual periods i. e., about two 

 hundred and eighty days at the end of which time birth takes place. 



The foetus is discharged from the uterus by powerful contractions of its 

 muscular walls, aided by simultaneous contractions of the diaphragm and 

 abdominal muscles. The first effect of the uterine contractions is to draw 

 the cervix on all sides tightly against the foetus and to dilate the passage way 

 until the child can be forced through. This stage of labor is called the 

 opening period', that following, which terminates in the complete discharge 

 of the offspring, is called the expulsion period. In cases of first births the 

 former period lasts about twelve hours, in subsequent births six hours; the 

 length of the expulsion period is estimated at two hours. These however are 

 only average figures, and the duration of birth may vary considerably 

 either way. 



Owing to their painful character the contractions of the uterus in child- 

 birth are commonly called labor pains. They are not continuous, but like 



FIG. 302. Normal curve of a contraction of the uterus, after Westermark. To be read from left 



to right. 



the contractions themselves are intermittent and become progressively longer 

 and more severe until near the culmination of labor. 



The frequency of labor pains is variable. At the beginning of the first 

 stage of labor, the interval between them is greatest, but it becomes steadily 

 less until it reaches its minimum (less than one hundred seconds) at the end 

 of this stage or some time during the second. When the pains are unusually 

 long and severe, the pauses are also longer. 



So long as there is no change in the volume of the contents of the uterus, 

 the intrant erine pressure during the pauses, as estimated by Schatz, Polallion, 

 Westermark, and others, remains remarkably even in any particular case of 

 labor ; but in different cases of labor it varies from 20 to 70 mm. Hg. When 

 the amnion is ruptured a decrease in the volume of the uterine contents takes 



