540 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



diphtheria, the epithelial tissues are subject to inflammations; in other 

 infections, for example syphilis, the endothelial tissues of the blood- 

 vessels undergo inflammation and sometimes proliferation. The epithe- 

 lial and endothelial cells are frequently actively phagocytic. Some of 

 the infectious microorganisms produce no effect whatever on these tissues 

 while others produce pronounced changes. 



Erythrocytes and Leucocytes. Lytic substances for the red blood 

 corpuscles are frequently produced in infections (haemolysins) . Strcpt. 

 pyo genes, M. pyo genes var. auretis, et al., and Ps. pyocyanea are among 

 the bacteria which produce haemolysins. Normal human blood and that 

 of some animals contains an antilysin for the staphylolysin and it is 

 sometimes produced in large amounts. Agglutinin substances for red 

 corpuscles are produced by some pathogenic microorganisms and it is 

 possible that these are the cause of the so-called agglutination thrombi 

 which occur in infections like typhoid fever. 



The most marked change seen in the leucocytes in infections is thei- 

 rather constant increase in number in most cases (leucocytosis) . In uncomr 

 plicated tuberculosis and typhoid fever, in measles and German measles, 

 in malaria and in dengue, there is no increase in number. In acute in- 

 flammations it is polymorphonuclear leucocytes that undergo increase. 

 This increase is sometimes preceded by a decrease (leucopenia) . The 

 leucocytes act as the principal phagocytes of the body and are attracted 

 (positive chemotaxis) to the bacteria or other microorganisms after they 

 have been sensitized by the opsonins in the body fluids. Besides acting as 

 phagocytes they may according to Metchnikoff produce antitoxins and 

 bactericidal substances. It has been suggested that the initial leucopenia 

 in some cases is due to negative chemotactic substances. Some virulent 

 bacteria cannot be phagocytized. 



Antibody Formation. One of the general effects of infectious micro- 

 organisms in certain infections is the production of antibodies of various 

 kinds. These may be antitoxins, as in the case of tetanus and diphtheria, 

 or bactericidal substances, as in typhoid fever and cholera, or opsonic 

 substances, as in the pyogenic infections. Agglutinins, precipitins and 

 other bodies are sometimes produced. 



