The data presented above indicate that the adreno-hemorrhagic and hypothermic factors are present only in certain groups of microorganisms. The differences in the reactions produced by the various groups of microorganisms seem to be due to their different chemical composition. Heavy reactions were produced by less than 1 mg of certain Eubacteriales, but could not be produced even by large amounts of organisms belonging to the Mycobacteria. In general, the hypothermic, hemorrhagic and leucopenic (cf. 1) reactions were associated, although they varied intensity; in the case of some organisms, 1 mg produced hemorrhages without hypothermia, and in others this amount produced hypothermia without leucopenia.

These reactions are influenced by unspecific factors, and there are also some differences in the sensitivity of the various laboratory animals. The leucopenic reaction appeared in guinea-pigs, as well as in rabbits, independently of the age of the animals. Rabbits weighing more than 2000 g showed severe leucopenic reactions. The other endotoxic reactions could be produced regularly only in guinea-pigs under 300 g. In addition, there exists an individually varying degree of resistance, the cause of which is not clear.

One injection of bacterial vaccine or of normal serum and plasma from rabbits or from guinea-pigs was followed by a period of nonspecific resistance to the injection of bacteria that contain the hypothermic and hemorrhagic factor. The hypothermic reactions were again elicited two or three days after the injection of the sera or 12 days after the injection of the vaccine. Within this period the hemorrhages appeared only in few animals. The leucopenic reactions could be prevented only for two days by the injection of vaccine, and in guinea-pigs, in contrast to rabbits, serum or plasma treatment was entirely ineffective. Thus, these animals showed isolated leucopenic reactions without hypothermia and without hemorrhages in the adrenals. This harmonizes with the greater sensitivity of the leucocytes to the action of the endotoxin.

In the active immunization experiments, the period of nonspecific resistance following vaccine treatment must elapse. Our tests were made 12 days after the last injection. Under these conditions some evidence for acquired resistance against the hypothermic action of bacterial vaccine could be obtained; there was, however, no indication that the adreno-hemorrhagic effect was influenced by the same amount of previous treatment with homologous vaccine.

In the passive immunization experiments, a period of at least two days must elaspe to exclude the nonspecific effect of the sera. After this period a specific protecting effect of the serum was not observed.

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