of Edinburgh^ Session 1865-66. 561 
lihood to have children, and specially a greater probability of being 
fertile than those married from fifteen to twenty. 
Wives who are persistently fertile are more fertile the older they 
were at the time of marriage. In other words, the older a woman, 
destined to he fertile, is at the time of marriage, the greater will be 
her fertility so long as it lasts. The fertility of a woman old at 
marriage is greater than that of a woman young at marriage ; yet 
the total fertility of women married young far exceeds that of 
women married when elderly, reckoning for both sets equal dura- 
tions of marriage, and all within the child-bearing period ; because 
of the younger a far larger proportion are fecund, and because the 
younger have a far longer continuance of fertility. 
The increasing frequency of twin-births as age advances is ex- 
plained by this law of increasing intensity of fertility as age 
advances. 
Women married when elderly have been supposed by some 
authors to have a special postponement of the generative orgasm, to 
enable them to bear children beyond ordinary periods. But this is 
shown not to be the case, by the circumstance that most women 
child-bearing at very high ages are already mothers of considerable 
families. 
2. On the Classification of Chemical Substances by Means 
of Generic Eadicals. By Dr Alexander Crum Brown. 
In this paper the author proposes to use for purposes of classifi - 
cation those radicals or parts of molecules which are common to 
genera of substances, and within which the changes characteristic 
of these genera take place. Thus the carbon acids contain the 
group or radical 
alcohols 
© 0 
M M 
Q— ; the aldehydes ©— and the 
d) (h 
d) 
© 
In the same way, as the acetones contain Li 
