4.The 1942 letter by Burrows was loaned to me in April 1955 by Dr Victor A McKusick (1921–2008), then Assistant Professor of Medicine at the Johns Hopkins Medical School. Dr McKusick later became chief of medicine at Hopkins and developed the field of human genetics. I made a typed copy of Burrows’ letter at the time, which was before photo copy machines. I was then a fourth-year medical student, working part-time in the tissue culture laboratory of Dr George Otto Gey (1899–1970), one of the early tissue culturists. At the top of my copy I had typed simply that the letter was ‘to an inquirer into his tissue culture work.’ No envelope was available and I did not copy the letter’s salutation. In 1955 I did not anticipate that 61 years later this letter would be of historical significance. Identification of the addressee would be interesting, but its absence does not diminish the historical importance of the letter’s content and Burrows’ own words. A search for the original letter was made in the Chesney Archives at The Johns Hopkins Medical Institution and was not found in the materials there relating to Dr McKusick or Dr Gey. Burrows died in 1947. Under the 1976 U.S. Copyright Act, copyright protection lasts for the life of the author plus 70 years. Thus, publication of Burrows’ letter should be legally permissible in 2017.