2 



And here must be mentioned another of tlie earlier theories, which 

 may be said to date back to Eichhorn in 1829, and which has received 

 more recent support from Buchner (1877) and Wolffberg (1885). This 

 may be termed the theory of local immunity, and supposes that during 

 infection the regions attacked by any specific disorder are so affected that 

 the weaker cells are destroyed, while those which have survived the 

 bacterial invasion transmit their resistant properties to their descendants. 

 But granting that this occurs locally, in diseases which have a purely 

 local manifestation, the supposition does not explain the immunity 

 acquired by unaffected parts of the same organ. Why, for example, 

 in ordinary vaccination, is not only the vaccinated area but the whole 

 skin and mucous membrane rendered resistant to variola 1 And 

 assuredly the theory cannot be applied to explain what may occur in 

 conuectiou with diseases like anthrax, in which subcutaneous inoculation 

 of the attenuated virus, the bacilli remaining localised, suffices not only to 

 give immunity against the cutaneous malady, but also prevents the onset 

 of the disease either by way of the respiratory or of the intestinal tract. 



These earlier theories must, therefore, be dismissed ; some wider 

 generalisation is demauded, a generalisation resting upon a more solid 

 basis of facts, and, as the discussion at the recent Hygienic Congress in 

 London abundantly proved, the question at present exciting the greatest 

 interest among bacteriologists is whether Metchnikoff's cellular theory 

 can adequately explain the known phenomena of the cure of infectious 

 disease and the production of immunity,* or whether, in addition to, or 

 apart wholly from the action of cells, the action of the bodily humours 

 must be invoked. Although the enthusiastic reception accorded to 

 Metchnikoff at the Burlington House meeting may have been but a 

 tribute to his ceaseless energy, a spontaneous and ungrudging acknow- 

 ledgment of the respect due to him for his laborious studies upon the 

 subject during the greutsr part of the last ten years, yet the heartiness 

 of the welcome seemed almost to indicate that the bacteriological world 

 is now nearly prepared to acoppt his theory with few reservations, and 

 that, in fact, among thooe competent to weigh the evidence, phagocytosis 

 has almost won the day. 



It is unnecessary nere to detail the observations upon intracellular 

 digestion in the invertebrata and lower vertebrata which led Metchnikoff 

 to study phagocytosis in its relation to the prevention of bacterial invasion; 



* The process of cura and resolution of infectious dise.ise and the processes conccrnod in tlie 

 production of immunity are of tiie same order of affairs ; it is impossible to draw any sharp line 

 of demarcation between the two. The conferment of immunity by means of attenuated virus ia 

 attended by local inflammatory action, and often by a feljrilo state of short duration — such as 

 Gamaleia has shown to be the inevitable attendant of successful inoculation of anthrax in 

 sheep, and as, to come nearer home, constantly attends successful vaccination against variola: 

 and similar disturbances attend the inoculation of powerful virus in animals already made 

 refractory. Thus, to quote Metchnikoff, " immunitt/ U most often but ncovcri/ in operation from 

 tin very onait of a disease." 



