NATURE OF THE ACTIVE PRINCIPLES 305 



amounts, on tlie average, to a three-fold increase in reacting po- 

 tency per nigni. of dry weiglit and nitrogen. (Shwart/man, Morell 

 and Sohotka, i9^^^7.) 



In tlie same investigation the bacterial filtrates were fraction- 

 ated by means of alcohol, acids, and alkalies (repetition of a 

 method used by Apitz for similar purposes) . By titrating the re- 

 covery of reacting factors it was found that the active principles 

 are ])rescnt in the nucleoprotein fractions, as weW as the alcohol 

 precipitated fractions. In spite of repeated re-precipitations of the 

 same material, the isolation of a biinet-negative fraction proved 

 impossible. The high nitrogen valties consistently fotmd in all 

 the active fractions suggested the presence of an appreciable 

 (piantity of protein-like substances. It appears, therefore, that the 

 active principles, similarly to exotoxins, are either protein-like 

 sid)stances or closely associated Avith proteins. The asstunption 

 that the molecides containing the active principles or associated 

 with it are of a large size is Avell borne out by the high antigenic- 

 ity of the active principles and the above mentioned dialysis ex- 

 periments. 



Here also a comparative sttidy may be in place on the mode of 

 production and certain other properties of the active principles 

 of the j)henomenon and true bacterial toxins. 



The heat resistance of true toxins has been considered, initil 

 recently, an important criterion for their identification, most of 

 the toxins being destroyed by exposure to 60° c. On the contrary, 

 the toxin of Streptococcus hemolyticus, ^vhich no doubt should 

 be included in the group of exotoxins, may withstand boiling for 

 a considerable length of time. The heat stability, however, de- 

 pends to a great extent on the mode of preparation of the filtrate. 

 Thus, it was shown by Hartley (1928) that concentrated and 

 ptnified Sreptococcus Jiemolyticus toxins are considerably re- 

 duced in potency by heating at 56° c. for one hour and are prac- 

 tically destroyed after one hour at 100° c. Bottdinus toxin offers 

 also a notable exception being considerably more heat resistant 

 than diphtheria and tetanus toxins. Thom, Edmondson and Gilt- 

 ner (1919) reported that botulinus toxin Avas destroyed in ten 

 mintites at 73° c. Schoenholz and Meyer (1925) obtained destruc- 

 tion in six minutes at 80° c. but these authors found that the toxin 

 produced by growth of B. hotiilinus in vegetables is still more 

 resistant. 



There seems to be little cpiestion that the active principles of 



