Record. xxix 



tioning, for about twenty-four hours, with cyanide of mer- 

 cury, followed for approximately the same length of time by 

 a formaldehyde solution, after which sections are cut, stained 

 with phosphomolybdate haematoxylin and, if desired, a con- 

 trasting stain, such as one of the aniline greens, and mounted 

 in the usual way. 



April 15, 1901. 



President Engler in the chair, thirty-two persons present. 



The Council reported that the Societe Scientifique et Medi- 

 cale de I'Ouest, of Rennes, France, had been added to the 

 exchange list of the Academy. 



Professor F. E. Nipher presented by title a paper On the 

 relation of direct to reversed photographic pictures, which on 

 motion was referred to the Council. 



Professor C. F. Marbut delivered an address on The ad- 

 vance made in geology during the nineteenth century. The 

 speaker discussed the earlier attempts to explain the structure 

 of the earth, describing the work of Weber, Hutton, Lyell 

 and Cuvier in establishing the chronological scale in general 

 acceptance to-day. The origin of volcanoes, the folding of 

 the earth's crust, the formation of mountains and the study 

 of the rocks were among the topics treated. 



Professor CM. Woodward spoke of An easy method of 

 determining the length of a generation. The speaker ob- 

 served that the average length of human life is often assumed 

 to be what is meant by a generation, but that it is quite a 

 different thing. The average length of human life in a given 

 community is readily found by averaging the ages of those 

 who die. The statistics for this purpose are given in mort- 

 uary reports. He had calculated that average from the An- 

 nual Report of the Board of Health of St. Louis, and had 

 found it to be between twenty and twenty-one years. The 

 length of a generation is the average difference in age 

 between father and son ; and it is at once evident that this 

 difference is equally independent of child mortality and of 

 longevity. Social and race conditions largely determine the 

 marriageable age and hence the length of a generation. The 



