A wide field of investigation is open to the patient Naturalist who will devote his energies to the study of that strange class of organisms, the parasites of man. Dr. Spencer Cobbold, the most eminent of British Helminthologists, who has recently honoured our local society by accepting the office of honorary vice-president, is now engaged in publishing, in the "Midland Naturalist," a series of papers in which he brings before our notice the fact, that the complete life-history of many human plagues is yet untraced. Here is full and useful occupation as have the necessary patience and application. The full career of some of them has been clearly demonstrated, through a series of metamorphoses more strange and bewildering than any we have read of in the fabulous pages of Eastern tale; wonderful as are the records of the Thousand-and-One Nights, no story related by Sheherazade is so full of marvel as that of the of varying phases of the life-career of a simple cestode worm. In unravelling the thread of such a career, and distinctly tracing it through all its changes, you may by some happy discovery of the peculiarities of one or other of these formidable guests, gain the proud distinction of having conferred a benefit on mankind. At present we know what fatal mischief they work upon their hosts but our knowledge is not sufficient to enable us to guard effectually against their unwelcome visits. It must be that, in a union of so many desirous of penetrating the secrets of nature, some by education and tastes are eminently qualified for this difficult pursuit. Its utility ought to be a sufficient inducement to follow it, and the absorbing interest it would generate in its followers would be their sufficient reward.
This special field of observation is not limited, as to its objects, to the ordinary entozoa and epizoa, which hitherto have been included in the lists of the Helminthologist; most of these are distinctly visible without the assistance of the microscope, which is only required for the examination of the details of their structure there is evidence of the existence of a large class of organisms, whose interference with our vital economy is far more fatal than that of ordinary parasites these are so minute as to tax the skill of the most expert histologists, and require the most perfect instruments to detect their existence. The generally accepted theory of their action appears to explain satisfactorily the course of many fatal diseases, as scarlet and other fevers, measles, smallpox, and, in fact, most of the diseases attributed to contagion but much more evidence is required to establish the theory on a firm basis. Already a large body of acute observers throughout the scientific world are engaged in pursuing this study; and the evidence obtained with reference to one particular form of disease splenic or relapsing fever appears to be conclusive, as numerous specimens of a peculiar form of Bacteria, called Spirilla, are always found to be present in the blood of persons while suffering from this fever, which disappear during the intermissions, and when the fever passes away. Other forms of Bacteria have been detected in the blood in other diseases but much evidence is still required to distinguish and identify them as the several causes of the mischief in the varying forms of contagion, the search for which will
