MENSTRUATION. 645 



left tube. This passage of an ovum from one ovary to the tube 

 of the opposite side is external migration, and is perhaps not as 

 infrequent as would at first be thought. Internal migration is the 

 passing of an ovum from an ovary down the tube of the same side, 

 through the uterine cavity, and to a greater or less extent up the 

 tube of the opposite side. Internal migration is supposed to account 

 for some tubal pregnancies. It is doubtful if it ever occurs. It is 

 to be remembered that the ovum is but 0.25 mm. in diameter, and 

 there seems no reason to question the power of the current to draw 

 so small a body into the tube. Once in the tube, it is carried on 

 to the uterus by the ciliated epithelium. 



Menstruation. At about the age of fourteen years a bloody 

 discharge takes place from the vagina at intervals of about four 

 weeks. This is the menses, and the process is menstruation. It 

 should be noted that the period of life at which menstruation 

 appears is by no means uniform in all individuals. 



Byron Robinson, in the Medical Brief, says that " the influ- 

 ences which change the individual age of beginning are : Climate, 

 race, residence, altitude, latitude and longitude, environments, 

 food, and disease. Climate (atmospheric and geographical rela- 

 tions) exercises the chief influence among the various factors. 

 In general, the hotter the climate the earlier the menstruation 

 begins. The average age for the beginning of menstruation is : 

 Chicago, fourteen ; Sweden, eighteen ; Norway, sixteen and one- 

 half; Denmark, sixteen and three-fourths; Russia, fourteen; 

 Germany, fifteen ; Great Britain, fifteen ; Austria, sixteen ; Pales- 

 tine, thirteen ; Turkey, eleven ; Syria, twelve ; Ceylon, Siam, and 

 Japan, thirteen." 



Prof. Skene, in his Diseases of Women, lays down the follow- 

 ing rules : 



1. Menstruation should begin at puberty that is, when the 

 woman is maturely developed, no matter what the age may be. 



2. It should recur at regular intervals : about every twenty- 

 eight days is the average time. A regular periodicity is normal, 

 but the duration of the periods often differs in different persons. 



3. The discharge should always be fluid in consistence and 

 sanguineous in color. 



4. The flow should continue a definite length of time, the 

 duration depending upon the habit of each case ; at least there 

 should not be any great deviation from this rule. The duration 

 is usually from three to five days, and the total amount is about 

 four or five ounces. 



At about the age of forty-five years menstruation ceases : this 

 is the menopause, or climacteric, or change of life. The cessation 

 is not abrupt, but gradual. The menstruation becomes irregular, 

 and finally ceases altogether. 



The changes which take place in the mucous membrane of 



