Although the pathological pigmentations form an extended series of alterations, the clinical importance of the condition may be regarded in many instances as trivial. The pigments resulting from extravasation produce no disturbance of function. The presence of bile-pigment does not account for the symptoms of jaundice. The clinical importance of melanæmia has perhaps been overrated. The earlier observations led directly to the inference that mechanical obstruction to the circulation in various organs might take place. The particles of pigment and the cells containing them were so numerous that this inference seemed quite probable. The evidence is still lacking, however, which proves the existence of definite symptoms and characteristic lesions as the result of the melanæmic condition. The inhaled foreign bodies, as coal and iron, are productive of greater disturbances, and are well known as efficient causes in the production of chronic pulmonary consumption. The coal-miner's and scissors-grinder's phthises usually have, as an anatomical basis, catarrhal conditions of the aërating surfaces and interstitial inflammations of the pulmonary connective tissue. Mechanical obstruction to the aëration of the blood may also be present from the extreme quantity of the foreign material in the lungs. Tuberculosis. Until the investigations and discoveries of the past few years, the presence of tubercles in the various organs and tissues of the body had been regarded as the essential element of tuberculosis. The evidence to be presented in the following pages will show that the immediate cause of tubercles may produce other lesions as well, and that the presence of a specific virus as the efficient cause of whatever may be the lesion, rather than the existence of tubercles, is to be regarded as the characteristic feature of the disease tuberculosis. The tendency of the present is to regard the latter term as including the various morbid processes connected with the origin, presence, and growth of a specific, organized virus, their dissemination, metamorphoses, and effects. Whether all those processes in connection with which the virus is found are due to the latter, or whether some may not arise and exist independently of the same, are among the questions whose answer is remote rather than at hand. As the presence of the cause of tuberculosis is the test demanded by some authorities for the existence of the process, so the anatomical classification has depended upon the existence of the tubercle. The substitution of tubercle for organized virus in the general definition of tuberculosis represents the distinction between the anatomical and the etiological classification of this affection. A tubercle was originally a small rounded body, a little tuberosity, and at the close of the last century the specific tubercle was distinguished from other rounded nodules.