The carbonaceous chondrites contain organic carbon. The word "organic" is not used in a biological sense, merely as a chemical term to describe compounds of carbon other than carbonates, bicarbonates, and carbides. No evidence has been found of any form of carbon other than organic, except for traces of carbonates. Various studies have demonstrated possible methods of estimating the total amount of organic matter present in meteorites. Wiik ([ref.27]) has suggested that organics can be estimated by measuring the loss of weight on ignition. Unfortunately, this method has several disadvantages and gives very low values. Corrections must be made for weight gains due to oxidation of reduced constituents, such as FeO, Fe, Ni, and Co, and for weight losses due to H₂O, S, etc. The water loss is exceedingly difficult to estimate, as part comes from the combustion of organic hydrogen and part comes from the loss of mineral-bound water. The carbon also proves difficult to combust completely, and high temperatures (over 1000° C) are required for efficient conversion to CO₂. In one study the major fraction of organic matter removed proved to have a carbon content of about 47 percent ([ref.28]). Thus, if all the meteorite carbon is present as organic matter of approximately this composition, total organics must be approximately double the carbon content; that is, 2 percent by weight carbon indicates 4 percent by weight organic matter. This estimate may be too low, for Mueller ([ref.29]) has extracted a major organic fraction containing only 24 percent carbon; however, this work has not been confirmed for other meteorites. Briggs and Mamikunian ([ref.26]) have pointed out that only 25 percent of the organic matter has been extracted, and only about 5 percent of this has been chemically characterized. Most of this 5 percent is a complex mixture of hydroxylated aromatic acids together with hydrocarbons of the aliphatic, napalicyclic, and aromatic series. Small amounts of amino acids, sugars, and fatty acids are also present. Thus far, these chemical analyses point to an abiogenic origin for the organic matter, and no conclusive evidence exists of biological activity on the meteorite parent body. Microbiological investigations of samples of the carbonaceous chondrites have yielded only inconclusive evidence on the problem of "organized elements." Several of these microstructures from different carbonaceous chondrites are illustrated in a paper by Mamikunian and Briggs ([ref.30]). It has been difficult to identify the organized structures, and most do not have morphologies identical to known terrestrial micro-organisms. However, they may prove to be a variety of mineral grains, droplets of organic matter and sulfur, as well as a small amount of contaminating terrestrial debris.