18 PRlNCiPLES Of VETfiRlNARY SURGERY 



ative process involves not only the making of new tissue cells, 

 but also the reriioval and absorption of the old. If the body 

 has been invaded by foreign substances, organic or chem- 

 ical, these also must be removed. 



The body possesses two principal means of disposing of 

 the tissue-debris and foreign invaders ; the leucocytes of the 

 blood and certain fixed cells have the power of ingesting 

 foreign substances, while the serous fluids of the blood and 

 tissues can wash them away through the lymphatics into 

 the general circulation. To this end the invasion of the body 

 by any foreign agent excites the circulatory system to sum- 

 mon its means of defense to the injured part. 



The changes ushered in by the processes of repair are 

 usually included among inflammatory processes. Instances 

 of simple destruction on the one hand, and simple regenera- 

 tion on the other are difficult to obtain. The injury to the 

 tissue is usually so great as to incite marked vascular changes 

 and these accompany every reparative process. They are 

 prompted by the irritating factor in the cause of the injury, 

 whether mechanical, chemical, thermal or bacterial, and vary 

 in degree according to the amount of irritation present. The 

 muscle-cells and endothelium of the vessel-walls, and the 

 corpuscles of the blood-stream are stimulated by the products 

 of irritation to which they respond somewhat as follows in 

 the process of healing: 



1. Dilatation of the Vessels. — This is most marked in 

 the arterioles and is also present in veins and capillaries. The 

 vessels may increase one-fourth larger than normal. 



2. Retardation of the Blood Current.— The axial cur- 

 rent of the stream becomes broader, leucocytes fall out into 

 the marginal stream, rolling slowly along. Stopping here and 

 there they finally come to a standstill, lodging in the wall of 

 the vessel. 



