president's address — SECTION L. 271 



a theory which could be applied to the whole field, to discover 

 some more or less important factor in the whole scheme and to 

 publish it promptly as the whole, comiplete and final. Again and 

 again these generalizations have proved inadequate, and with a 

 host of workers attacking the problems of immunity froan all 

 sides, and in light of all the magnificent contributions to our 

 knowledge during the past three or icixr decades, we now know 

 that the factors in immunity are not few, but many; that the 

 defence of the body against attack by invaders, of whose multi- 

 farious devices we arei becoming increasingly aware, is not one-sided, 

 simple, direct, but made up of a wealth of adaptations, of agents, 

 materials and methods of which we are now becoming dimly 

 cognisant. A very wise aphorism of Bordet's might with advan- 

 tage be taken tO' heart by all workers in this field. He says, "In 

 deciding the role of each antibody in the total power of the serum, 

 leave a sufficiently generous part to the unknown." 



For the immediate study of immunity of the body against in- 

 fections disease it might be thought that investigation confined 

 to the actual infective agents, their j^roducts, and their effects, 

 would concentrate attention on the kernel of the problem and 

 hasten its solution. At the outset, however, it soons becomes 

 clear that the dc-monstration of the presence of various antibodies 

 in the blood of an immune animal qualitatively and quantitatively 

 is not easy. The chemistry of these bodies is very obscure, their 

 physical properties are complex. It is therefore a matter of 

 great importahoe to) discover cl\aracteristic reactions, if possible 

 obvious to the naked eye, which will serve as indicators of their 

 presence and activity. From this will be understood the great 

 advance which followed Bordet's discovery that red blood cor- 

 puscles of an animal of one species injected on three or four 

 occasions intoi an animal of another species would give rise to the 

 production in this second animal of an antibody, a hapmobjsin, 

 capable of liberating the haemoglobin from the red cells of the 

 ammal donor, a reaction quite obvious in the test tube. Here, 

 then, is an exaniple of an animal immunized against foreign cells, 

 and its immunity is evidenced by the production of an antibody 

 capable of combining with the cells against which it has been 

 immunized. These foreign cells constitute in fact an "antigen," 

 a producer of antibody, and may be taken as a type of antigens 

 in general. 



In a similar way light has been thrown upon the nature of 

 toxins, anti-toxins and their mode of combination by experiments 

 using some of the vegetable toxins, of which ricin, the toxin from 

 castor oil beans, may be taken a-s a type. Study of the actions 

 of various snake venoms has also contributed to our understanding 

 of the natui'e of toxins and anti-toxins. 



