On the basis of the author’s theory the phenomena of protein immunity and antianaphylaxis may be explained in the following way which the author has not seen presented. The enzymes necessary to decompose the injected protein are present in certain cells and are formed in larger amount by those cells to meet the increased demand due to injection of an excess of protein. They are retained in the cell for a time at least. If a second dose of protein is given before the enzymes are excreted from the cells as waste, this is digested within the cells in the normal manner. If a third dose is given, the cells adapt themselves to this increased intracellular digestion and it thus becomes normal to them. Hence the _immunity_ is due to this increased intracellular digestion. On the other hand, if the second injection is delayed long enough, then the _excess_ enzyme, but not all, is excreted from the cells and meets the second dose of protein in the blood stream and rapidly decomposes it there, so that more or less intoxication from the split products results. This uses up _excess_ enzyme, hence subsequent injections are not digested in the blood stream but within the cells as before. So that “antianaphylaxis” is dependent on the exhaustion of the excess enzyme in the blood, and the condition is _fundamentally_ the same as protein immunity, _i.e._, due to _intracellular_ digestion in each case. As has been indicated “serum sickness” and sudden death following serum injections are probably due to a sensitization of the individual to the proteins of the horse in some unknown way. Probably hay fever urticarial rashes and idiosyncrasies following the ingestion of certain foods--strawberries, eggs, oysters, etc., are anaphylactic phenomena.