From the preface of the book, To secure absolute conformity to truth and reality I have photographed, what in these days of micro-organisma must be called the coarser microscopic constituents of sputum, and have had the negatives employed to illustrate this work reproduced by a process named "Photogravure" which, while equal in clearness and crispness to silver-printing, has the great advantage of being perfectly permanent; its only drawback is its expensiveness, which is so serious as to have caused the omission of many illustrations I had intended to introduce. This task of photogravuring has been successfully accomplished by Messrs Annan & Swan, of London and Glasgow to whom it was entrusted… All the photographs have been prepared from specimines selected as typical, and the Hospital for Incurables has furnished me with inexhaustible materials for investigation, and for sifting the truth or error of preconceptions and opinions, sometimes adopted too hastily an on too inadequate grounds. [1]