The lipoidic character in this homologous series starts with the five carbon valeric acid, although caproic acid is the first lipoidic member found in animals. The role of the saturated fatty acids in organization is largely related to the activity, as caloric metabolites, of the members with even carbon numbers. These saturated fatty acids are absorbed, circulated and stored as triglycerides, and it is also this bond to glycerol which apparently favors their biological role as caloric metabolites.

As previously noted, only the members with a relatively short chain, less than 12 carbons, can be directly metabolized through Knoop beta oxidation. Longer chain saturated fatty acids undergo a breakdown before further metabolic degradation. Members with 16 and more carbons also play a limited constitutional role, usually together with an unsaturated member, when bound to glycerophosphoric acid to form phospholipids. Even when free—that is, when their polar group is not neutralized—they do not have a manifest functional role and, consequently, show no important pharmacodynamic activity.

The higher fatty acids exert no demonstrable influence upon microbes nor upon viruses such as bacteriophages. No influence has been observed upon monocellular organisms, cells or tissues in vitro. No changes were seen in the respiration of liver slices or of Sa 180 ascites cancerous cells in the Warburg microrespirometer. Similarly, no influence can be seen on red blood cells nor on leucocytes treated in vitro. No changes in the chloride content of tumors or wounds are induced by administration of these acids. The fact that no change could be induced in the second day wound crust pH explains the lack of any effect upon pain.

Even large doses, such as 20 cc. of a 10% solution of these acids in sesame oil, do not change the intensity of pain of alkaline or acid pattern in humans. No influence has been noted upon tumor evolution, even with the direct technique of dipping tumor transplants in the agent, repeated for successive transplants. Existing edema or ulceration is not influenced. At the organic level, no changes can be seen in the function of various organs or upon liver regeneration rate. These fatty acids do not influence convulsions induced by thiamine in rats even when administered in very large doses, such as 5 cc. or more of 10% solutions for 100 gr. of body weight. The same lack of influence is seen on systemic metabolic manifestations, as recognized through various analyses. Except for palmitic acid, which shows an adrenal defense index of 12, the index for the other members of this series is below 6, indicating only a certain participation of the adrenals in the defense mechanism against these acids.

No changes can be found in the number or character of leucocytes in animals treated for a few days with these acids. No change in the sodium or potassium content of the blood or in urinary analyses is induced by these substances even in subjects whose analyses reveal abnormal patterns. No action upon body temperature and no influence upon the evolution of the defense mechanism can be observed.

It is interesting however, to note the effect of the sodium salts of these acids, especially on in vitro lysis of different cells. (Note 1)