The steady advances of biochemistry and immunology have been disclosing the presence of the same complex compounds, some of them being known as possessing remarkable physiologic effects, in apparently unrelated living entities. Omitting vitamins and the common enzymes, the cases of some sex hormones, cardiac glucosides and the Forsman antigen may be suggested as representative examples.
Recently another interesting example involving a system of a powerful enzyme and its specific substrate has been added to the list. Hyaluronidase, best known and most important of the "spreading factors,"1 is present abundantly in invasive bacteria such as staphylococci, pneumococci and some anaerobic gas gangrene bacteria, in the poisonous secretions of snakes and insects, in leeches and in the testes and sperms of mammals. By hydrolizing hyaluronic acid present in the cement between the cells of the connective tissues, the gelatinous fundamental substance of the mesenchyme, the enzyme brings about a spreading