It is classically accepted that the intestinal absorption and circulation of fatty acids is made through bonding to various substances. The analysis of this absorption shows, however, that different fatty acids have preferential bonds. For saturated and monoethenic fatty acids, the bond is principally with glycerol. Although mono- and di glycerides can be identified in the cells of the intestinal mucosa, these fatty acids leave the intestine as triglycerides, forming the largest part of the chylomicrons. They are also found in reserve in adipous cells as triglycerides. The di-, tri- and even tetraenic fatty acids usually enter the circulation as phospholipids, that is, in direct combination with glycerophosphoric ions. The polyunsaturated acids are bound to sterols when they enter the blood, circulate and are stored. While the structures of the various fatty acids determine their different roles in the organism, it is the anti fatty acid constituents to which they are bound which enhance these roles. The study of the anti fatty acids has shown that these substances can even dictate, by themselves, different fates for the various fatty acids they bind.

The combination of glycerol with any fatty acid seems to establish a caloric metabolic character. This is true for the very different fatty acids found in plants and animals as triglycerides. Even the ricinoleic triglyceride, if fresh, is used as comestible oil, castor oil. The same is true of the oil of triglycerides of polyunsaturated fatty acids found in marine animal oils. In the seeds, all the triglycerides of fatty acids, even the conjugated ones such as eleostearic and parinaric, represent energetic sources. It seems that it is their combination with glycerol which has given all these fatty acids value as caloric metabolites. The same is true for the bond to glycerophosphoric ion.

Combination with glycerophosphoric acid endows various fatty acids with the ability to participate in the construction of membranes. The bond to sterols, on the contrary, induces an ultimate functional activity provided the fatty acid itself is so constituted as to be able to fulfill this function.

The influence exerted by anti fatty acids can be understood in terms of the changes they induce in the activity of the fatty acids. Since the activity of the last is largely related to their presence as free substances, it is principally through their combination with fatty acids that the anti fatty acids intervene. By inactivating those free fatty acids which form a membrane and insure its permeability, an anti fatty acid agent can cause the membrane to change its permeability and even to become completely impermeable. Similarly, an anti fatty acid, by combining with a polyunsaturated fatty acid, can reduce or even suppress its functional activity. It is to be noted that, by both changing permeability and suppressing functional activity, the anti fatty acids exert their influence ultimately by altering oxygen metabolism. From this point of view, metabolism becomes predominantly anoxybiotic in contrast to normal oxybiotic metabolism. For glucose, for instance, suppression of the oxidative phase arrests metabolism at pyruvic acid which passes into lactic acid. The appearance of acid substances as a biological effect of the action of anti fatty acids results, in fact, from the reduction of the fatty acid's activity, affecting oxidative processes directly, or indirectly through reduction of membrane permeability.

While one group of anti fatty acids can be directly related to hydroids, and especially to glycerol or to glycerol bound to phosphoric acid as in the glycerophosphoric ion, a second group is represented by lipoids, principally formed by derivatives of a characteristic ring system, the cyclopentano phenanthrene. As anti fatty acid lipoids, these compounds, the steroids, were of special interest in lipoid research. Only some aspects of the biological activity of steroids—mainly, those which represent new views in the study of these substances—will be discussed here.