548 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



been previously discussed. In all probability the tears are only slightly 

 antiseptic, not germicidal at all. The conjunctiva is sometimes infected 

 with microorganisms and furthermore serves as a point for entrance of 

 microorganisms into the body when it itself is not infected. The Bad. 

 influenza, the Strept. pneumonia and other microorganisms may enter 

 the body and get into the lymphatic and blood circulation in this way. 



It it seen therefore that the protection afforded an individual by 

 the body surfaces is a decided factor in the natural immunity of that 

 individual. 



The Protective Nature of Inflammatory Processes. It has been 

 mentioned in a previous discussion that, when bacteria successfully enter 

 a tissue and develop in that tissue, a complex local change results which 

 we designate as inflammation. In many instances inflammation is of a 

 beneficial nature. Fundamentally, it is always beneficial. It is question- 

 able whether there are many examples of pernicious results from inflam- 

 mation. In this connection may be mentioned the thickening of the 

 cerebral blood vessels in syphilis and the increase of connective tissue in 

 cirrhosis of the liver. In these instances the inflammatory processes are 

 brought about by the reaction of the various tissues to the irritation of the 

 infecting microorganisms. Unluckily these reactions are not, on the whole, 

 beneficial to the body, but, as before stated, inflammation is usually 

 beneficial and may be characterized as the reaction of tissues to injury. 

 The exact process of inflammation may be traced in case an infecting 

 microorganism succeeds in entering the tissues of the body. The 

 organism having produced its toxic substance first causes a congestion 

 of the bloodvessels in the region (hyperaemia). Following this localized 

 congestion there is an extravasation of plasma from the blood vessels. 

 This plasma immediately on leaving the vessels coagulates or clots, 

 producing throughout the infected area fibrin and blood serum. This 

 fibrin serves in a mechanical way to limit the infection, and it has been 

 recently demonstrated that the fibrin possesses germicidal properties 

 in addition. Furthermore, the serum in a large number of instances 

 exerts a bactericidal effect upon the microorganisms. Following the 

 extravasation of blood plasma from the capillaries, the leucocytes 

 pass out to gather about the infected area. These leucocytes are 

 attracted to the area due to the presence in the bacteria of various 

 chemical substances (chemotrophism) . They will come as close to the 

 microorganism as possible, depending upon the effect of the toxins 



