My introductory treatise on the Entozoa having long been out of print, it occurred to me that instead of attempting another edition it would be better to write an entirely new work, employing only such fragmentary portions of the old treatise as would harmonise with the far wider design I have now in view. Whilst, therefore, I have freely utilised a selection of the illustrations given in the elementary volume, comparatively few of its pages have been incorporated in the present work.

Dealing with parasites and parasitism after a manner not hitherto attempted I have purposely omitted minute anatomical descriptions, and, with rare exceptions, I have avoided the introduction of clinical details. While bringing to a focus the records of, and principal references to, a widely scattered, intricate, and voluminous literature, it has been my chief endeavour to supply abundance of original matter of a kind that cannot be found in the columns of any existing treatise. Whether I have succeeded or not the experienced helminthologist alone can judge. He, at all events, will perceive that the summary, though compressed within the space of a moderate-sized octavo, can only have resulted from sustained effort.

This treatise is not professional, that is to say, it does not concern itself with therapeutics or the curative treatment of parasitic affections; yet it introduces and helps to solve many questions relating to epidemics, endemics, and epizoÖtics due to parasites. The medical man who only looks at the phenomena of parasitism as displayed within the human territory must of necessity acquire a cramped, narrow, and distorted conception of the rÔle played by parasites in the production of disease. Let it be freely granted that to the practising physician, as such, it matters little how many beasts, birds, reptiles, or fishes perish annually from parasitic affections; yet, when it is demonstrable that a large proportion of the strictly human entozoa require a change of hosts—or, in other words, need to pass through the bodies of the lower animals—then it is evident that some acquaintance on his part with the entozoa infesting animals becomes a practical necessity. Knowledge of the kind here offered will often materially aid him in recommending prophylactic measures. Moreover, the study of comparative pathology, almost ignored in England, conveys with it other lessons of high value in relation to the healing art. The great mind of John Hunter comprehended all this long ago, as any student of the beautiful preparations contained in the museum of the Royal College of Surgeons may readily convince himself; and this is all the more noteworthy, since the subject concerns the physician rather than the surgeon.

To the naturalist the second half of this book addresses itself in a very direct manner. When engaged in his dissections, an appeal to its pages will often enable him to decide at once as to the species of parasite accidentally encountered, and if a full diagnosis be demanded it will guide him to better sources of information. Many hundreds of correspondents, not having ready access to the systematic writings of Rudolphi, Diesing, and Dujardin, have requested me to identify their “finds.” I have rarely or never failed to comply with their requests; but it is hoped that the present work may prove of ready service to subsequent inquirers, and thus place a reasonable limit upon the number of future applicants. Since the manuscript of this work was completed I have received Dr von Linstow’s Compendium der Helminthologie, which, for the purposes held in view by the author, leaves little to be desired.

Expressly to meet the requirements of the Sanitarian I have dwelt upon the developmental phenomena exhibited by those parasites that occasion fatal helminthiases; and, in this relation, I have not confined my remarks to the parasites that are injurious to man in a direct manner, but have extended my observations to the genesis of those entozoa that prove destructive to horses, to beasts of burden generally, and to other creatures which, like cats and dogs, are in various ways subservient to man’s wants. It will be seen that in this way several questions relating to the purity of water and flesh-food, respectively, have been incidentally brought under notice.

In view of the magnitude of the task which my enthusiasm, perhaps unwarrantable, has led me to undertake, I know full well how considerately my foreign friends and correspondents will deal with the errors of omission and commission that they will certainly detect in these pages. If there be any educated persons at home who still affect to despise the revelations of helminthology, I can assure them that their prejudices are misplaced. The study of the structure and economy of a humble parasite brings to the investigator no slight insight into the workings of nature. If these workings cannot at all times be pronounced to be “good and beautiful,” they must at least be characterised as “true.” The knowledge of the true—especially if that knowledge by its practical applications be calculated to confer substantial benefits upon man and his inferior fellow-creatures—ought to be held in high esteem; but, apart from this purely utilitarian view, there remains for the investigator the delight occasioned by the in-rush of new scientific ideas. The average mind, being either essentially commercial or ridiculously sentimental, as the case may be, is totally incapable of comprehending the motive power that animates and guides the votary of science. The late Professor Faraday, a man wholly untinged by the ambitions of wealth and power, once remarked to me that there were no people so difficult to instruct as those who were ignorant of their own ignorance. It is just these very persons who, when placed in high positions of social, political, or professional trust, most powerfully contribute to check a nation’s progress. There are too few genuine workers at science in this country. As one of the rank and file, I claim only to have honestly contributed my mite. I should like to see a small army of helminthologists rise up and lay siege to the fortresses at present securely held by thousands of death-dealing parasites.

T. S. C.

74, Portsdown Road, London
May, 1879.