It is worth the time and money to one who wishes to use vaccines to learn from one who has had experience both in making and administering them, and then to remember that each patient is an individual case, for the use of vaccines as well as for any other kind of treatment. AGGRESSIN. Opsonins have been shown to be specific substances which act on bacteria in such a way as to render them more readily taken up by the leukocytes. By analogy one might expect to find bacteria secreting specific substances which would tend to counteract the destructive action of the phagocytes and bactericidal substances. Bail and his co-workers claim to have demonstrated such substances in exudates in certain diseases and have given the distinctive name “aggressins” to them. By injecting an animal with “aggressins,” antiaggressins are produced which counteract their effects and thus enable the bacteria to be destroyed. The existence of such specific bodies is not generally accepted as proved. The prevailing idea is that bacteria protect themselves in any given case by the various toxic substances that they produce, and that “aggressins” as a special class of substances are not formed. CHAPTER XXXI. ANAPHYLAXIS. Dallera, in 1874, and a number of physiologists of that period, observed peculiar skin eruptions following the transfusion of blood, that is, the introduction of foreign proteins. In the years subsequent to the introduction of diphtheria antitoxin (1890) characteristic “serum rashes” were not infrequently reported, sometimes accompanied by more or less severe general symptoms and occasionally death--a train of phenomena to which the name “serum sickness” was later applied, since it was shown that it was the horse serum (foreign protein) that was the cause, and not the antitoxin itself. In 1898 Richet and Hericourt noticed that some of the dogs which they were attempting to immunize against toxic eel serum not only were not immunized but suffered even more severely after the second injection. They obtained similar results with an extract of mussels which contain a toxin. Richet gave the name “anaphylaxis” (“no protection”) to this phenomenon to distinguish it from immunity or prophylaxis (protection).