_Adulteration._--The chief adulterations of oysters are the “floating” above described and the treatment of the “shucked” oysters with formaldehyde, boron compounds, and other preservatives to keep them from spoiling. These processes are thoroughly reprehensible and are rapidly disappearing. The consumer who lives near the source of supply should never eat any but freshly shelled oysters and those at a distance confine themselves to the properly prepared and shipped article. The chief delight of the epicure is the freshness, and not the quantity of nourishment of this justly prized bivalve. _Average Composition of Oysters:_[19]-- Water, 60.08 percent Solids, 39.92 „ Nitrogen, 1.56 „ Phosphoric acid, .42 „ Sulfur, .19 „ Fat, 9.48 „ Ash, 1.77 „ Protein, 9.73 „ [19] Average of samples used at Hygienic Table, Bureau of Chemistry. ANIMAL OILS. The same distinction is made between oils and fats for animal products as has been made for the vegetable preparations further on. An animal fat remains solid or semisolid at the ordinary temperature of the living room. An animal oil, on the other hand, is one which at ordinary temperature is a liquid. Animal oils, as a rule, are not used for edible purposes directly, but are used to some extent in cooking, and to a large extent as medicinal food. Inasmuch as these oils are used for medicinal food purposes, those which are most important in this use may be very properly described in this manual. As these oils are derived both from sea and land animals they are often conveniently divided into marine animal oils and terrestrial animal oils. There is also a marked difference as a rule between the oils of marine origin and those of terrestrial origin. The oils of marine origin, as a rule, have a very high iodin number while the animal oils of terrestrial origin have an iodin number not much greater than the fats from which they are derived. This distinction corresponds somewhat closely to those vegetable oils which belong to the drying and non-drying variety. The iodin number represents the percentage of iodin absorbed by a unit weight of substance. If one gram of an oil absorb 0.67 gram of iodin, the iodin number is 67. The marine oils correspond to the dry vegetable oils and the terrestrial oils to the non-drying vegetable oils. While this difference is one which is marked, it does not always exist in each individual case. MARINE ANIMAL OILS. The marine animal oils may be conveniently divided into fish oils, liver oils, and blubber oils. Of these the liver oils are the most important from an edible point of view or a medicinal edible point of view. The fish oil and blubber oil are used chiefly for illuminating and other technical purposes.