It may now be regarded as a well established fact that cellular antibody alone is responsible for the reaction known as acute anaphylactic shock. There are, however, certain other manifestations of anaphylaxis which are with difficulty explained upon that basis, and on this account many conservative workers incline to the belief that under certain circumstances circulating antibody may also play an important part in the production of the symptoms. At first sight it might not appear to be a matter of great consequence whether the interaction between antigen and antibody takes place within the cells, or in the fluids of the body. Such, however, is far from the fact. The humoral theory requires the assumption of an intermediary toxic product, a hypothetical anaphylatoxin, which secondarily affects the cells. The cellular theory does not require such an hypothesis.