In inflammation all three irritative processes occur side by side. Indeed, we may frequently see that when the organ itself is made up of different parts, one part of the tissue undergoes functional or nutritive, another formative, changes. If we consider what happens in a muscle we see that a chemical or traumatic stimulus produces a functional irritation of the primitive fasciculi, with contraction of the muscle followed by nutritive changes. On the other hand, in the interstitial connective tissue which binds the individual fasciculi of the muscle together, real new formations are readily produced, commonly pus. In this manner the three forms of irritation may be distinguished in one part. The formative process is always preceded by nutritive enlargement due to irritation of the part, and has no connection with irritation of the nerves. Of course there may be also an irritation of the nerves, but this, if we do not take function into account, has no causal connection with the processes going on in the tissue proper, but is merely a collateral effect of the original disturbance. Besides these active processes of function, nutrition, and new formation, there occur passive processes. Passive processes are called those changes in cells whereby they either lose a portion of their substance, or are so completely destroyed, that a loss of substance, a diminution of the sum total of the constituents of the body is produced. To this class belong fatty degeneration of cells, affection of arteries, calcification, and ossification of arteries, amyloid degeneration, and so forth. It will now be necessary to consider inflammation at more length. The theory of inflammation has passed through various stages. At first heat was considered as its essential and dominant feature, then redness, then exudative swelling; while the speculative neuropathologists consider pain the _fons et origo_ of the condition. Personally, I believe that irritation must be taken as the starting-point in the consideration of inflammation. We cannot conceive of inflammation without an irritating stimulus, and the first question is, what conception we are to form of such a stimulus. An inflammatory stimulus is a stimulus which acts either directly or through the medium of the blood upon the composition and constitution of a part in such a way as to enable it to attract to itself a larger quantity of matter than usual and to transform it according to circumstances. Every form of inflammation with which we are acquainted may be explained in this way. It may be assumed that inflammation begins from the moment that this increased absorption of matters into the tissue takes place, and the further transformation of these matters commences. It must be noticed that hyperaemia is not the essential feature of inflammation, for inflammation occurs in non-vascular as well as in vascular parts, and the inflammatory processes are practically the same in both instances.