The "Lateral-chain Theory" of Immunity 119 



glutinate 'aggregate them in clumps and sensitize them to the 

 future action of other phagocytes by which they may be taken 

 up. Through extensive phagolysis, and the liberation of large 

 quantities of the enzyme contents of the phagocytes into the blood, 

 the plasma and serum acquire a "fixing" or "sensitizing" quality 

 from the macrocytase of the macrophages, which is the "fixateur" 

 or "substance sensibilisatrice" and a bacteria-dissolving quality 

 forms another enzyme, microcytase, from the microphages. Thus, 

 we find that Metschnikoff is prepared to account for the "ambo- 

 ceptor" or "immune body" of Ehrlich, which is the macrocytase, 

 and the "complement," which is the "microcytase" In cases 

 where the bacteria exert a negatively chemotactic influence upon 

 the leukocytes, no immunity exists. 



The antitoxins are similarly accounted for by Metschnikoff: the 

 cellular digestive enzymes exert their action not only upon the 

 microparasites, but also upon their products, fixing or otherwise 

 altering them until they can be finally destroyed. 



It will thus be seen that the two chief theories of immunity, though 

 they appear discordant when explained independently of one 

 another, can be fairly well harmonized. Ehrlich believes the im- 

 mune bodies to be the products of those cells of the body with whose 

 haptophile combining groups the haptophore groups of the antigen 

 engaged, and does not attribute the function to any particular 

 group of cells; Metschnikoff attributes all the activities to the 

 phagocytes, and especially the leukocytes. Ehrlich looks upon the 

 phenomena as chemical and pictures them as taking places inde- 

 pendently of the cells; Metschnikoff looks upon them as vital and 

 brought about by the agency of living cells. Both theories are 

 ultimately chemical. 



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

 may, by reversing the hypothesis and 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 amplified by Welch in his Huxley Lecture, f The micro- 

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

 for combination 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 

 producing neutralizing bodies. These neutralizing bodies by which the defenses 

 of the host are broken down are among those described by BailJ as "aggressins." 



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



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



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

 18, 1902. 



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

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



