ACQUIRED IMMUNITY 133 



absence of toxins but after a space disappear, leaving 

 behind only the power of tolerating the toxins, only the 

 power of readily producing digestive bodies when stimulated 

 by toxins. 



211. The serum treatment, whether employed by nature, 

 as in syphilis, or by man, as in diphtheria, supplies digestive 

 substances, and attenuated toxins. In the hands of nature 

 the digestive substances are probably of primary importance, 

 as there is then an unlimited supply of them from the mother 

 on the one hand, and on the other a weak capacity for pro- 

 ducing them in the infant. When, however, man seeks to 

 secure acquired immunity artificially the digestive substances 

 in the antitoxin are doubtless of comparatively little import- 

 ance. They are limited in quantity and are soon exhausted. 

 The attenuated toxins, not only when the serum treatment 

 is employed, but also in protective vaccination against small- 

 pox, rabies, and anthrax, are then of primary importance. 



212. The foregoing theory of immunity carries us a very 

 little way. It merely supposes that acquired immunity is a 

 physiological reaction, 1 a use-acquirement of the same nature 

 as other use-acquirements. Some of these use-acquirements 

 are quantitive; the organs or tissues acquiring them in- 

 crease in size. Others are qualitative ; the organs or tissues 

 increase in power. Many are both quantitive and qualitative ; 

 as when a muscle not only increases in size, but to a dis- 

 proportionate extent in capacity for doing work. No doubt 

 in the last analysis most qualitative changes are, to some 

 extent at least, quantitive ; 2 this or that constituent of the 

 part which has undergone change is increased or diminished 

 in amount. But as yet we are far from being able to deter- 

 mine the quantitive changes, if any, which occur when a 

 nerve cell becomes used to nicotine or even to such a simple 

 substance as alcohol. And we are just as far, I imagine, from 

 being able to determine the precise changes which occur 

 when phagocytes and other cells become used to this or that 

 toxin. 



1 It is hardly necessary to state that the writer claims no originality 

 for the hypothesis that acquired immunity is a physiological reaction. 

 It has been a commonplace in bacteriological literature (see, for instance, 

 the most admirable article by Dr. Kanthack in Professor Clifford 

 Allbutt's System of Medicine). 



2 They cannot always be merely quantitive as stated by Weismann 

 (The Germ-plasm). Thus when a cell dies the change is qualitative 

 but can hardly be said to be quantitive. 



