108 INFLAMMATION. 



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elated with some form of injury. This may be direct trauma, or exces 

 sive heat or cold. It may be poisons of various kinds from the cruder 

 inorganic poisons inducing immediate and gross tissue destruction to the 

 subtle toxic substances which result from the metabolism of micro-organ- 

 isms or from the aberrant metabolism or degeneration of the body cells 

 themselves. 



Let us now look at some of the ways in which the living body re- 

 sponds to injury, and first at an injury which is very slight and simple. 



Types of the Inflammatory Reaction of the Body to Injury, 



Injury to Non-Vascular Tissue. If a small clean cut be made in liv- 

 ing fibrillar connective tissue, not involving blood-vessels and affecting 

 only the cells and fibres in the vicinity of the incision, and if the sides 

 of the wound be immediately placed and held together, the resulting 

 changes which lead to the complete restitution of the part are compar- 

 atively simple. A small quantity of fluid which oozes from the tissue 

 spaces sticks the sides of the cut together. Such connective-tissue cells 

 as have been seriously injured, especially if the nuclei have suffered, die 

 and disintegrate. But cells whose nuclei have remained intact, whether 

 directly upon the incision or in its immediate vicinity, become larger and 

 more granular, may divide by mitosis, extend their bodies or processes 

 across the plane of incision, bridging this at intervals with living proto- 

 plasm. Under the influence of these cells, new intercellular fibres are 

 formed, which in a short time bind the sides of the wound firmly together. 

 Thus with but the slightest amount of tissue destruction, and with no in- 

 volvement of the blood-vessels, a simple mechanical injury may be made 

 good. This form of reaction to injury of living tissue is known to the 

 surgeons as healing by first intention. The mode of healing does not essen- 

 tially differ if there be a slight injury to the blood-vessels. 



Injury to Vascular Tissue. Let us now look at the effect on a vascular 

 tissue of an injury not immediately destructive. For this purpose the 

 mesentery or the bladder of a curarized frog, drawn out upon a suitable 

 plate upon the stage of the microscope and kept moist by irrigation with 

 three-fourths-per-ceut salt solution, affords a succession of most instruc- 

 tive pictures. The mechanical disturbance of the organs exposed, desic- 

 cation, and a variety of other physical and chemical vicissitudes to 

 which they are subjected are sufficiently damaging to incite a complex 

 train of responses on the part of the living tissues. 



In studying the circulation of the blood in small vessels under the 

 microscope it should be remembered that, while the walls of these ves- 

 sels are made up of living tissue and are capable of responses by move- 

 ment or by structural change to external agencies, whether applied direct- 

 ly or through the nerves, they are also elastic pipes through which fluid 

 flows, and that both pipes and fluid are subject to the laws of mechanics. 

 These mechanical laws are often modified in expression, it is true, by the 

 subtle energies which living tissues wield, but, as Thoma more than any 



