Such are the returns as recorded by Dr Thomas. If a comparison be instituted between the data supplied by his decade-report and those supplied by the decade-report which I have previously adduced (p. 123), it will be seen that as regards the returns for the years 1868-72, inclusive, both reports are in perfect agreement. Of still more interest also is the circumstance that whilst, on the one hand, out of the total of 307 deaths given in Dr Thomas’s table, 116 occurred during the first semi-decade (_i.e._ from 1868 to 1872, inclusive), on the other hand, no less than 181 deaths occurred during the second semi-decade (_i.e._ from 1873 to 1877, inclusive). This increase of 45 deaths during the later semi-decade is very significant. It points either to the fact of more careful returns having been made, or to an actual increase in the fatality of the disorder. Possibly both the causes alluded to operated to affect the returns. Be that as it may, Dr Thomas’s record is highly instructive, and should stimulate the profession in England to supply our Registrar-General with more precise data wherewith to construct his annual reports. BOOK II. PARASITES OF ANIMALS. In dealing with this division of the subject it will be impossible to give more than the faintest outline. Let it be borne in mind that quite as much information might be offered by me respecting the parasitism of each of the commoner domestic animals as has been already advanced in regard to the helminthism of man. That would by no means exhaust the subject. Thus treated, a score of volumes, each equal in size to this, would barely suffice to cover the whole ground of Parasitology; and yet there are not wanting intelligent persons who regard Helminthology as unworthy of their attention. These persons form a far too prevalent type of educated ignorance, and unfortunately, it is just this class of people who enjoy the prerogative of educational responsibility. Even our metropolitan scientific institutions, expressly raised for the purpose of diffusing useful knowledge, shrink from the revelations of parasitism. Dominated by the miserable conception which judges that the life-history of a worm cannot prove either interesting or instructive to their audiences, they let slip the acquisition of scientific data, a knowledge of which might enable them to combat successfully some of the most terrible evils to which human flesh, in common with that of animals, is heir. In the following few pages many new points of departure for fresh scientific work will inevitably be suggested; and if I only succeed in conveying to the working student an adequate grasp of the whole subject, especially in its bearings on the welfare of the higher domesticated animals and man, I shall have accomplished all that I can reasonably hope to do within the restricted limits of space at my command. SECTION I (MAMMALIA).