1. The neutral fats, fatty acids, and lipoid bodies of serum seem to play no part in autodigestion. Neither the addition of fats or lipoids in excess to the serum, nor their removal by extraction with ether influences the phenomenon of autodigestion.
2. There is present in native serum an antienzymic substance which is closely related to the autolytic ferment of serum.
3. The antiseroprotease of normal serum has almost the same thermal resistance as the seroprotease; that is, it survives heating at 55°C. for 30 minutes but is completely inactivated at 60°C. for the same length of time.
4. The ferment can be removed from the serum by means of inorganic adsorbents, but the antienzymic substance remains in the treated serum.
5. The autolytic power of the sera of man and other animals is much weaker than that of guinea pig serum, but they contain as much as does the latter of the antisubstance which inhibits the digestion of the activated guinea pig serum.
6. The autodigestion of the activated serum is due to the splitting of the serum protein by the proteolytic ferment of the same serum and is brought about by the destruction of the antienzymic substance by the chemical reagents. On the other hand, the digestion products in a mixture of a foreign substrate and guinea pig serum are derived from the direct digestion of the substrate by the serum ferment. This digestion takes place in spite of the presence of the antiseroprotease. The serum separated from the substrate can no longer produce a split product, but is as actively antienzymic as the original serum and undergoes autodigestion only when treated with acetone or other chemical activators.