The term inflammation (from inflammo, I set on fire), is suggestive of the local heat of the inflamed part, just as fever (febris) indicates an elevation of the temperature of the body at large. Celsius enumerated the features of rubor, calor, dolor and tumor (redness, heat, pain and swelling) which have come down to our own time as at least suggestive of inflammation. But any diagnosis, based on these alone, would be today woefully inadequate. Redness occurs in the transient blush, heat in the febrile state, though no inflammation can be recognized, pain is present in neuralgic and other nervous affections, and swelling in dropsy and tumor. On the other hand redness is entirely absent, for a time, after the outset of inflammation in nonvascular tissues (cornea, articular cartilage), the heat of the inflamed part may be actually lowered when there is much exudation around the capillary vessels and lessened flow of blood, pain may be absent in some circumscribed inflammations of the lungs, and swelling is not at first visible in the inflamed cornea or compact bony tissue. These phenomena which are so common in inflammation and, in general so characteristic of it, cannot therefore be accepted as infallible evidence of its existence, nor can their absence be held as absolutely implying its nonexistence. =Forms of Inflammation.= This morbid process might be divided almost indefinitely according to the organ invaded, the cause, and type, yet it will be more convenient to deal with it generically and notice =inflammation in nonvascular and vascular tissues= respectively, and the different types of =granular degeneration=, =exudative inflammation= and =croupous inflammation=. It will be requisite further to notice an =acute= and a =chronic= type. By dealing first with the changes in the anatomical elements of the tissues and in the innervation, we shall virtually cover the phenomena observed in nonvascular tissues, and later the changes in connection with the circulatory system will give the additional characteristics of inflammation in vascular tissues. CHANGES IN THE TISSUE ELEMENTS. =Death of cells and tissue.= By the application of an irritant (acid, heat, etc.,) a certain thickness of tissue with its enclosed cells is killed, and a thin layer of necrosis is usually produced. This does not constitute inflammation, but it acts as a foreign body, often septic, in producing inflammation in the parts adjacent.