Agassiz had published another book in America, in 1848, "Principles of Zoölogy," which had a large sale, and was much used in schools. In 1849, his only son, fifteen years old, came to live with his father. The following year, 1850, Agassiz married Elizabeth Cabot Gary, of Boston, a cultivated and lovely woman. His daughters, much younger than their brother, arrived from Europe the same year. M. Christinot, though urged to remain, now preferred to find another home, settled in New Orleans as pastor, and later died in Switzerland.
The winter of 1851 was spent in the examination of the Florida reefs and keys, a work undertaken at the request of Prof. A. D. Bache, at the head of the United States Coast Survey. The results were valuable in showing "how far the soil now building up from accumulations of mud and coral débris was likely to remain for a long time shifting and uncertain, and how far and in what localities it might be relied upon as affording a stable foundation," for building lighthouses, etc. Agassiz brought back for his museum a fine collection of corals, of all varieties and in all stages of growth, with drawings made on the spot, from the living animals.
This year he accepted a professorship at the medical college in Charleston, S. C., lecturing during the three winter months, between his autumn and spring courses at Cambridge. The overwork finally resulted in a dangerous illness, and he was obliged to discontinue it in 1853. The year previous he received the Prix Cuvier for his "Fossil Fishes." His fond mother wrote: "This has given me such happiness, dear Louis, that the tears are in my eyes as I write it to you."
He now issued a circular asking for collections of fishes from various fresh-water systems of the United States, and responses came from every direction. New England captains, when they started on a cruise, took out cans, furnished by Agassiz, for collections in distant ports. Fishermen and farmers, indeed all classes, heartily joined in coöperating with the man who had said in the University at Munich, "I will be a leader of others," and he had reached the mark which he set for himself. In 1854 he was urged to accept a professorship in the recently established University of Zurich, Switzerland; but he declined, for he had one definite aim in America, to found a great museum, where the best methods of study could be adopted. He said in his "Fossil Fishes": "Possessing no fossil fishes myself, and renouncing forever the acquisition of collections so precious, I have been forced to seek the materials for my work in all the collections of Europe containing such remains; I have, therefore, made frequent journeys in Germany, in France, and in England, in order to examine, describe, and illustrate the objects of my researches; but, notwithstanding the cordiality with which even the most precious specimens have been placed at my disposition, a serious inconvenience has resulted from this mode of working, namely, that I have rarely been able to compare directly the various specimens of the same species from different collections, and that I have often been obliged to make my identification from memory, or from simple notes, or, in the more fortunate cases, from my drawings only. It is impossible to imagine the fatigue, the exhaustion of all the faculties, involved in such a method." He hoped to found a museum where students should have specimens for work, ready for their use.
