I 3 4 THE PRINCIPLES OF IMMUNOLOGY 



piece combines only at considerably higher temperatures. It has also 

 been found that the mid-piece of one animal species may be activated 

 by the end-piece of another animal of the same or different species. 

 Nevertheless, Ritz and Sachs have shown that the serum of an animal 

 may possess a mid-piece for certain sensitized erythrocytes, but does 

 not necessarily possess a corresponding end-piece. Marks has studied 

 the quantitative relations of mid-piece and end-piece and has found that 

 a ratio of i-i is not necessarily the optimum for hemolysis and that 

 very often it is necessary to change the ratio; this change must be by 

 increase of mid-piece, never by increase of end-piece. If the two 

 are mixed before addition to the amboceptor-cell mixture, an excess 

 of mid-piece inhibits hemolysis, but if the excess of mid-piece is added 

 first followed by end-piece, hemolysis is complete. Brand and later 

 Hecker found that if the globulin precipitate is preserved dry or in 

 solution in distilled water it will retain activity for several days, but in 

 physiological salt solution it loses its activity in three to four hours. 

 This, however, does not indicate destruction of mid-piece in salt solu- 

 tion since it will combine with sensitized cells if added before end- 

 piece. Marks holds that this phenomenon is due to the inhibition of 

 hemolysis by excess of mid-piece and does not occur if proper pro- 

 portions are maintained in the mixture. Swirski maintains that the 

 complement fixation of the Wassermann test binds mid-piece but not 

 end-piece. This has been investigated by Bronf enbrenner and Noguchi, 

 who believe that the free end-piece in Wassermann tests differs from all 

 other end-pieces in that it activates the complex which includes sheep 

 cells but has no effect upon the cells of other animals. Bessemans has 

 recently investigated again the question of thermostability of end-piece 

 and mid-piece. He finds that there are important differences in certain 

 of the sera he has examined, so that a general statement in regard to the 

 heat resistance of these fractions is not justified. 



Browning and Mackie have found that by various methods of f rac- 

 tioning the serum it is possible to divide complement into four frac- 

 tions and that certain combinations consisting, as a rule, of at least three 

 of these reproduce quantitatively the full hemolytic effect of the whole 

 complement. This presents numerous intricate possibilities of experi- 

 ment, but the important point is that such a demonstration makes the 

 use of the terms mid-piece and end-piece no longer desirable. 



Normal Hetero-hemolysins. The preceding discussion has been 

 concerned chiefly with complement and immune amboceptor. Histori- 

 cally much study had been directed toward the normal cytotoxic powers 

 of blood serum before the immune amboceptors were recognized; 

 Fodor, Nuttall, Nissen and Buchner had investigated the action of nor- 

 mal sera in dissolving bacteria. Buchner in 1893 pointed out a similar 

 capacity of blood serum for dissolving animal cells, particularly ery- 

 throcytes. Ehrlich and Morgenroth took up the question as to whether 

 or not the globulicidal activity of normal serum is due to an interaction 

 of two substances similar to that in immune sera. They showed that 

 normal dog serum is capable of dissolving guinea-pig erythrocytes, but 



