128 CHEMICAL EQUILIBRIA 



Two Greatest Systems of the IVorld GALILEI makes 

 his representative SALVIATI say that the hypothesis 

 of a daily motion of the earth is much better than 

 the many hypotheses regarding the Ptolemaic 

 epicycles and cite the words of ARISTOTELES : 

 " Frustra fit per plura quod potest fieri per pauciora," 

 or, freely translated: "We ought to use as few 

 hypotheses as possible in our explanations." This 

 principle, which is also adopted by NEWTON in his 

 Principia, is fundamental in all scientific work, and it 

 will also give the decision regarding the "plurality- 

 hypothesis " in immuno-chemistry regarding anti- 

 diphtheric serum. 



If we inject the red blood -corpuscles from 

 an animal into the veins of an animal of another 

 species, we find after a certain time of incuba- 

 tion three days or more (cp. p. 15) an antibody 

 which haemolyzes blood -corpuscles of the same 

 kind as the injected ones in this animal's blood- 

 serum. If we heat this haemolysin to 55" C. for 

 some minutes it is " inactivated," i.e. it loses its 

 haemolytic power. But this inactivated fluid still 

 contains some active substance, for it regains its 

 haemolytic power after addition of a normal serum- 

 in most cases fresh serum from guinea-pigs is used- 

 which itself possesses a very small haemolytic power. 

 Some substance in this fresh serum is not specific, 

 but acts against all kinds of erythrocytes, "completes" 

 the inactivated serum, and is therefore called the 

 "complement," whereas the active substance in the 

 inactivated serum, which is specific against the in- 



