In the study of morbid processes, therefore, one must appreciate the normal conditions and manifestations of life in the individual. Physiological laws govern pathological phenomena, and the latter must always be submitted to the tests furnished by the former. Just as little, however, as the study of anatomy familiarizes the student with the anatomical changes resulting from diseased processes, does the study of physiology accustom the student to the features of disease. Pathological processes must be studied by themselves and for themselves, although the means which are employed may be the same as those used in physiological research. It is evident that the exactness of method which is the demand of the physiological investigator cannot be secured by the pathologist. The material of the latter lies farther, beyond his control. Nevertheless, much of the ground to be gone over is common, and the object sought for is essentially the same--the knowledge of the conditions necessary to maintain life. In an introduction to the study of disease there are certain processes which deserve early recognition. They are both the cause and the result of disease, and may occur in various diseases, either limited to one organ or present in a series of organs. Their treatment at present obviates the necessity of repetition, and prepares the reader for the special consideration of their occurrence in the various structures and systems of the body. These processes are named in virtue of some prominent characteristic, and each is made up of a complex series of conditions and disturbances. In part, they represent modifications in the circulation of blood and lymph; in part, they consist of nutritive derangements, whose consequences appear as the various degenerations, or as the additions to the body, the new formations. The processes and groups of processes in question are those included under the following heads: inflammation; thrombosis and embolism; effusions; degenerations; tuberculosis; and morbid growths. {37} Inflammation. Inflammation is characterized now, as in the time of Galen, by the presence of redness, heat, swelling, and pain. The disturbance of function, added to modern definitions, is to be regarded either as a result or a cause, or both, of the variously modified physiological processes whose sum is the inflammation. The redness of inflammation is obviously dependent upon the presence of an increased quantity of blood. This is readily apparent in the direct observation of the blood-vessels of an inflamed, transparent part of the body, as the mesentery of the frog or rabbit, or the tongue and webbed foot of the former animal. The redness of inflammation consequently demands the presence of blood-vessels in the affected region, and becomes all the greater the more vascular the part--_i.e._ the richer it is in such vessels.