Nott advanced the theory that yellow fever was caused by minute animalcula. Reproduced in part in R. H. Major, Classic descriptions of disease, 3rd ed., 1945, p. 122.

Nott, a prominent physician and anthropologist in Mobile, Alabama, employed polygenist arguments to justify slavery. This required resoilving the problem of racial hybridity. Polygenists claimed that different races were different species. Species, however, were supposed to be incapable of producing fertile offspring, while it was obvious that different races, specifically white and black could reproduce and create mulattoes. To keep the designation of races as 'species' intact, Nott redefined the definition of species, making its essential characteristic not hybrid infertility, but morphological distinctness through time-time longer than could be inferred from the Bible. . . . Nott sought to disassociate anthropology from the Bible. His alternative explanation was that races had been separately created before Biblical time. His medical experience convinced him that blacks and whites possessed different susceptibilities to disease, attributable to innately different 'vitalities.' Nott argued against monogenist anthropologists, who believed that races had a recent and common origin. . . .Nott's comments on race brought him to the attention of other members of the American School, including its proclaimed leader, Samuel George Morton. After Morton's death, George Glidden, then the U.S. consul in Cairo, persuaded Nott to co-author a book, Types of mankind, dedicated to Morton's memory. Gliddon's contribution was to show that blacks and whites had been distinct as early as Egypt's first dynasty. Nott's contribution was also intended to demonstrate the antiquity of racial differences, as well as to show that races were immune to major change. Digital facsimile of the 1854 second edition from the Internet Archive at this link. Sttee Paul A. Erickson, The anthropology of Josiah Clark Nott avaiable from digitalassets.lib.berkeley.edu at this link.

Expensively produced, and sold in both standard and large paper subscriber editions, Nott and Gliddon's work was one of the most egregiously racist publications in the history of physical anthropology. Nott, a prominent Southern physician, was a member of Samuel George Morton's American School of Anthropology, which held that that the different races of humankind represented separate species with separate, ancient origins predating the Biblical "creation." Polygenist arguments about race were particularly attractive in the antebellum South, as they provided support for slavery without overtly contradicting the Bible's account of the creation. One of the most outrageous of these arguments (by our standards) was Agassiz's correlation of the geographical distribution of monkeys with that of the "inferior" (i.e., non-white) races of man, an idea further developed by Gliddon in a fold-out chart. This chart, as well as the large folding "Ethnographic Tableau" at the front of the book, are hand-colored in the subscriber's edition; in the regular small-paper edition they are uncolored. Digital facsimile  of a "Subscriber's Copy" from the Internet Archive at this link.