146 Immunity 



substances exactly as do the cells of the host. As the host reacts 

 toward the active products of the bacteria, so the bacteria react toward 

 the defensive products of the host, and as the cells of the former are 

 stimulated to the production of immune bodies that shall facilitate 

 bacteriolysis, so the latter are stimulated to antagonize their action by 

 producing neutralizing bodies. These neutralizing bodies by which 

 the defenses of the host are broken down are among those described 

 by Bail* as " aggressins." 



Thus, as the cells of the host invaded are constantly reacting to the 

 active bodies produced by the invading parasites, so the latter are re- 

 acting toward the defensive products of the former. If the reactive 

 processes of the host predominate, immunity and the destruction of 

 the parasites result; if those of the bacteria predominate, increased 

 virulence, facilitated invasion, and death of the host may result. This 

 hypothesis also serves to make clear why micro-organisms entering the 

 body not infrequently show a marked tendency to colonize in certain 

 organs and tissues in preference to others. 



Supposing accident to determine the tissue in which the primary in- 

 fection has taken place, a longer or shorter residence in that tissue, 

 with the resulting more or less marked acquired immunity against the 

 defensive activities of that tissue, endow the organism with a higher 

 degree of virulence for it than for other tissues, so that if at some 

 future time the organism entering the circulation of a new host were 

 able to colonize in any tissue of the body, its activities could be 

 more easily and more successfully manifested in that to which it had 

 already become accustomed, and to which it had acquired a peculiar 

 adaptability. This adaptability has been made the subject of inter- 

 esting experimental demonstration by Forssnerf in his work upon the 

 intravenous injection of streptococci. 



SPECIAL PHENOMENA OF INFECTION AND IMMUNITY. 



Certain phenomena which present themselves in the course 

 of infection and immunity, to which reference has already 

 been made, must now be considered in detail. These are 

 Specific Precipitation, Agglutination, Antibody Formation, 

 and Cytolysis. 



I. Specific Precipitation. In 1897 Krausi in studying- 

 the "specific reactions produced by homologous serums with 

 germ-free filtrates of bouillon cultures, of cholera, typhoid and 

 plague bacteria," observed that immune serum brought into 

 contact with the respective culture filtrate occasioned a 

 precipitate specific in nature, to which he gave the name 

 "specific precipitate." It thus became known that in ad- 

 dition to antitoxins, bacteriolysins, and agglutinins, other 

 specific bodies were formed. 



Bordet and Tchist o witch || showed that the phenome- 



*" Wiener klin. Woch.," 1905, Nos. 9, 14, 16, 17; " Berl. klin. 

 Woch.," 1905, No. 15; "Zeitschr. f. Hyg.," 1905, Bd. I, No. 3. 

 f'Nordiskt Medicinskt Archiv," Bd. xxxv, p. 1, 1902. 

 J "Wiener klin. Woch.," 1897, No. 32. 

 "Ann. de 1'Inst. Pasteur,'.' 1899, p. 173. 

 |] " Ann. de 1'Inst. Pasteur," 1899, p. 406. 



