Special Phenomena of Infection and Immunity 123 



The fundamental ideas embodied in the "lateral-chain theory" of immunity 

 may, by reversing the hypothesis a-nd considering the bacterial instead of the 

 body 'Cells to be upon the defensive, be made to explain other phenomena of 

 immunity. Walker* seems to have been the pioneer in this field, and his 

 researches show that it is possible to immunize bacteria against "immune 

 serums" by cultivating them in media containing increasing proportions of the 

 immune serums. The bacteria thus cultivated were of increased virulence. 

 The idea was further ajnplified by Welch in his Huxley Lecture, t The micro- 

 organismal cells must be regarded as endowed with receptors of their own, fitted 

 for combinaton with adapted haptophorous elements in the juices reaching 

 them, and therefore capable of reacting toward such 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 facili- 

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

 ducing neutralizing bodies. These neutralizing bodies by which the defenses of 

 the host are broken down are among those described by Bailt 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 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, 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 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 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 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 Kraus|| 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." 



*"Jour. of Path, and Bact.," March, 1902, vra, No. i, p. 34. 



t "British Medical Journal," Oct. 11, 1902, p. 1105; "Medical News," Oct. 

 18, 1902. 



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

 No. is; "Zeitschr. f. Hyg.," 1905, Bd. i, No. 3. 



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



II "Wiener klin. Woch.,'" 1897, No. 32. 



