I20 Immunity 



bodies produced by the invading parasites, so the latter are reacting toward the 

 defensive products of the former. If the reactive processes of the host predomi- 

 nate, immunity and the destruction of the parasites result; if those of the bacteria 

 predominate, increased virulence, faciUtated 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 infection 

 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 enteriiig 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 interesting experimental demonstra- 

 tion by Forssner* 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, 

 casually made, must now be considered in detail. 



SPECIFIC PRECIPITATION 



Specific precipitation is the coagulation or precipitation of an anti- 

 gen by its specific antibody. In 1897 Krausf while 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." 



Bordetf and Tchistowitch§ showed that the phenomenon was 

 of wide occurrence and had a broad significance, for they discovered 

 that when the serum of one animal was injected into another ani- 

 mal of different kind, some reaction took place in the injected ani- 

 mal, which caused a precipitate to form whenever the serums of 

 the two animals were being .subsequently brought together in a 

 test-tube. The same was found true of milk. When an animal was 

 injected with the milk of a different kind of animal, its serum ac- 

 quired the property of causing a precipitate to form when its serum 

 and filtered milk were mixed together in a test-tube. The substance 

 or factor inducing the precipitation was called "precipitin" or 

 "coagulin." Myers,|| Jacoby,** Nolf,tt and others showed that 

 the faculty of provoking specific precipitins was common to many 

 albuminous bodies — albumen, globulin, albumose, peptone, ricin, 

 etc. Kraus in his original communication dwelt upon the specific 

 nature of the precipitation, and was corroborated by Fish, J J Wasser- 



* "Nordiskt Medicinskt Archiv," 1902, Bd. xxxv, p. i. 



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



X "Ann. de I'Inst. Pasteur," 1899, p. 173. 



§ "Ann. de I'Inst. Pasteur," 1899, p. 406. 



11" Centralbl. f . Bakt.," etc., 1900, Bd.xxxiii, and "TheLancet," 1900, 11, p. 98. 

 ** "Archiv fur exper. Path. u. Pharmak.," 1900. 

 tt "Ann. de I'Inst. Pasteur," 1900, p. 297. 

 %% "Courier of Medicine," St. Louis, Feb., 1900. 



