238 THE BIOLOGY OF HYDRA : 1961 



weight basis are expressed relative to an arbitrary standard, bovine 

 liver acetone powder. Activity was found in micro-organisms as 

 well as in crude mammalian tissues. Substances with no demon- 

 strable activity when fed internally included vitamins, amino acids, 

 protein digests, nucleic acids, carbohydrates, and microbiological 

 media. 



An active soluble preparation, bovine liver extract, was sub- 

 jected to a number of physical and chemical tests in an effort to 

 characterize the active constituents. The results of such tests are 

 shown now in Table 3. The activity was found to be non-dialyzable, 



TABLE 3 

 Potencies of modified non-dialyzable soluble extract 



and was destroyed by ashing, characteristic of an organic macro- 

 molecule. Heating in solution precipitated but did not destroy the 

 active material. Incubation of the extract with trypsin or chymo- 

 trypsin resulted in the disappearance of nearly all biological ac- 

 tivity. The ultra-violet absorption spectrum of the soluble extract 



TABLE 4 

 Potencies of ammonium sulfate fractions of non-dialyzable soluble extract 



'Fraction precipitated between the indicated points of saturation. 



