REACTIONS OF NEWBORN AND ADULT ORGANISMS 527 



to any extent with the production of hemolysins following subcutaneous in- 

 jections of sheep red blood corpuscles. In more recent investigations Jules 

 Freund as well as Leona Baumgartner noted that production of agglutinin, 

 hemolysin and precipitin, interacting with bacteria, erythrocytes or proteins, 

 is less intense in very young rabbits, and according to Baumgartner, the avidity 

 of immune sera for antigenic bacteria may be diminished. Furthermore, the 

 skin in very young rabbits is less sensitive than in adult ones, and in young 

 guinea pigs the skin likewise reacts less actively to tuberculin. However, as 

 stated, at present we cannot entirely exclude the possibility that in some cases 

 a previous infection with a homologous or heterologous microorganism may 

 have caused an increased resistance against certain viruses or bacteria. 



As to the mode in which a physiological maturation of cells leads to an 

 increased resistance, Hirszfeld is inclined to attribute it to an increase in 

 affinity of cells for certain toxins, taking place either during a normal bio- 

 chemical maturation process or as the result of the previous activity ojf 

 microorganisms and their toxins. Such an increase in affinity of cells for a 

 certain antigen is also assumed to be the factor causing anaphylactic reactions. 

 Thus during the process of immunization there may exist, side by side with 

 the production of antibodies, an increased sensitiveness to the action of toxins. 

 If children, negative to the Schick or Dick tests, who are allergic to the toxins 

 of diphtheria bacilli or of streptococci, are actively immunized by the injection 

 of these respective microorganisms or their toxins, their skin may for some 

 time react positively to the local injection of the toxins and thus a change may 

 take place, which is apparently due to an increase in the affinity of certain cells 

 for the products of these bacteria. 



From a purely chemical point of view, very little is known as to the changes 

 occurring in cells with increasing age, although it has been shown that there 

 are alterations in the water content and in the amount of calcium and 

 cholesterin or its esters held by certain tissues during the process of ageing. 

 Furthermore, Kossel has shown that during maturation of the sperm cells 

 their constituent proteins undergo definite variations as far as the quantitative 

 distribution of the amino-acids and diamino-bases (histidin, lysin, arginin) 

 is concerned. According to Schenk, the character of the globin in the hemo- 

 globin changes during the ageing of the erythrocytes or in persons affected by 

 pernicious anemia. Thus it becomes conceivable that the mode of reaction of 

 certain cells to homoiogenous sera or to toxins may differ under various 

 conditions, and especially at different ages and during the process of im- 

 munization; but the chemical character of the factors underlying the change 

 in the mode of reaction is not definitely known. 



It may then be concluded that the differences in reaction towards homoiog- 

 enous or heterogenous tissues which organisms show at different stages of 

 development and at different ages are not an isolated phenomenon, but are 

 the expression of changes in reactivity to various types of foreign substances, 

 especially to those of a toxic character. In general, both the reactivity of cells 

 against foreign substances and the ability of tissues to produce immune sub- 

 stances against them is lacking or diminished in young organisms. Presumably 



