122 Immunity 



quires a "fixing" or "sensitizing" quality from the presence 

 of the "fixateur" or "substance sensibilisatrice." The 

 actual solution of the bacteria is accomplished by the 

 "microcytase" of the leukocytic phagocytes. Thus, we 

 find that Metschnikoff is prepared to account for the "am- 

 boceptor" or "immune body" of Hhrlich, which is the 

 fixateur, and the "complement," which is the "microcytase." 

 When the phagolysis is excessive, either from infection or 

 intoxication, both the fixateur and microcytase are free in 

 the serum. In cases where the bacteria exert a negatively 

 chemotactic influence upon the leukocytes, no immunity 

 exists. The reactive phenomena occasioned by the intro- 

 duction of tissue elements and blood-corpuscles, depend upon 

 enzymes derived from the macrophages, the "fixateur" as 

 before, and "macrocytase." 



The antitoxins are similarly accounted for: the cellular 

 digestive enzymes exert their action not only upon the 

 organized complex molecules of the microparasites, but also 

 upon their more simple toxic products, fixing or otherwise 

 altering them until they can be finally destroyed. 



It will be seen that the two chief theories, though they 

 appear discordant when explained independently of one 

 another, are fairly well coordinated. Ehrlich believes the 

 active bodies to be the products of those cells of the body 

 for whose haptophorous combining groups the haptophorous 

 groups of the active bodies 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 independently 

 of the cells; Metschnikoff looks upon them as vital and 

 brought about by the agency of living cells. 



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

 immunity may, by reversing the hypothesis and considering the bacte- 

 rial instead of" the body cells to be upon the defensive, be made to ex- 

 plain 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 



*"Jour. of Path, and Bact.," vin, No. 1, p. 34, March, 1902. 

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

 News," Oct. 18, 1902. 



