1. The lipoid fractions from the tubercle bacillus contain maturation factors for monocytes, epithelioid cells, and epithelioid giant cells.

2. The most important component of the lipoids for biological investigation is the phosphatide A-3, since this produces the most massive reaction toward epithelioid cells and epithelioid giant cells, and also because it is the only partition of the lipoids which acts as an antigen.

3. The stimulus to the formation of tubercles resides in certain fatty acids of high molecular weight found in tubercle bacilli. These fatty acids are present in the four major partitions of the lipoids and account in each instance for their specific activity. The most potent fatty acid in the production of tubercles is that derived from the phosphatide. The purified, optically active phthioic acid obtained from the glyceride fraction, in small dosage produces epithelioid cells, but more non-specific connective tissue; the optically inactive tuberculo-stearic acid is relatively inert.

4. The specific tubercular tissue resulting from the intraperitoneal injection of the phosphatide from the tubercle bacillus undergoes resorption. Two mechanisms in its disappearance similar to those operating in the disease have been seen: caseation in which masses of degenerating epithelioid cells become infiltrated with leucocytes; phagocytosis of the cellular debris by clasmatocytes, without caseation.

5. Beside the specific reaction of the lipoids, these also produce a marked growth of non-specific connective tissue cells, without, however, any reaction toward fibrous tissue in the acute stages. All the subfractions from the lipoids are irritating when injected into the peritoneal cavity, calling leucocytes into the tissues and stimulating clasmatocytic activity. The unsaponifiable substance from the purified wax is particularly active in producing an extreme general reaction of connective tissue cells.

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