22 Predisposition and Immunity. 



and Sachs, have, however, brought forward facts hitherto unsus- 

 pected and of the greatest interest in this connection, and have 

 pointed out not merely theoretical hypotheses upon immunity, but 

 also practical methods of extreme value in combating the in- 

 fectious diseases. 



As already pointed out, there already pre-exist in the normal 

 blood of every animal certain substances capable of dissolving 

 foreign material which has in some way gained entrance, and, by 

 entering into combination with resultant toxic matter, of render- 

 ing it harmless. In some of the glands, as the thyroid and liver, 

 neutralization of toxic matter and noxious metabolic products is 

 being continually carried on ; and when one considers the innu- 

 merable reactions ;and interactions which are taking place in 

 metabolism, resulting in the most varied types of secretory ma- 

 terial with destructive and digestive properties, it is easy to think 

 of the body and each of its cells as a chemical laboratory of 

 manifold productive ability. 



In attempting an explanation of the m.echanism involved in 

 the production of these antibodies (antagonistic or protective 

 substances), Ehrlich has proposed a brilliant, and, at first thought, 

 a very convincing theory, the chief points of which are briefly 

 included in the following. The hypothetical details of this theory 

 have recently met such serious objection at the hands of Gruber 

 that in a great measure it seems but doubtfully credible. The 

 basic fact that antitoxines and protective substances are products 

 of the cells and organs of the body is not endangered by this 

 criticism, but the problem of how and where such substances are 

 formed is renewed as a matter for further investigation. 



According to this view the cells of the body may be thought 

 of as organisms which consist of a basis of protoplasm, which 

 has as its vital center a nucleus (vital nucleus of Ehrlich) ; 

 this protoplasmic unit may be fancied as being possessed about 

 its periphery of armlike processes, the receptors or side-chains of 

 Ehrlich. [It is to be understood here that the author refers to 

 the protoplasmic molecules as the basis of this theory, each mole- 

 cule being composed of a more or less complex group of atoms 

 or of combinations of atoms. The vital center does not refer to 

 the nucleus seen as a structural part of the cell, but to the struc- 

 tural nucleus of such a complex molecule of its protoplasm. As 

 is attempted in the graphic chemical formula of a complex or- 

 ganic molecule with the symbol C as its center, to indicate as 



