Injection of endotoxin of Gram-negative bacilli into NCS mice caused an immediate reduction or interruption of water intake by these animals, with a resultant loss of body weight.

Endotoxins prepared by three different techniques from four different cultures of Gram-negative bacilli yielded products having approximately the same activity in inhibiting water intake. The minimum effective dose was 0.1 µg. or less. With all toxin preparations tested, the duration of the effect was directly related to the dose injected.

The heat-killed cells of Esch. coli proved approximately as effective as the endotoxins prepared from Gram-negative bacilli. In contrast, heat-killed cells of Mycobacterium tuberculosis (BCG) were much less active, and heat-killed cells of Staphylococcus aureus were essentially inactive.

Mice previously treated with endotoxin exhibited a marked degree of tolerance to the inhibition of water intake caused in normal animals by a subsequent treatment with the same material. Tolerance could also be induced by vaccination with heat-killed Gram-negative bacilli. Tolerance overlapped from one bacterial species to another but was more pronounced toward the endotoxin prepared from the bacterial culture with which the animal was vaccinated.

The duration of the inhibitory effect of endotoxin on water intake was much shorter with mice fed a complete diet than with mice fed a deficient diet (corn).

It took approximately the same dose of endotoxin (0.1 µg.) to inhibit water intake, reduce the influx of polymorphonuclear leucocytes, and enhance staphylococcal infection.

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