_Properties._--Cod liver oil at 15 degrees has a specific gravity of .922. Its iodin number varies very greatly but is always high, ranging from 150 to 180. Its refractive index is also very high, namely 1.47. An important constituent of cod liver oil is cholesterol. Cod liver oil contains naturally a small quantity of iodin and this natural compound of iodin is one of the properties to which much of its medicinal virtue has been attributed. The quantity present is extremely minute, and probably never exceeds .002 of one percent. _Adulteration of Cod Liver Oil._--Owing to its increasing price cod liver oil has been subjected to many forms of adulteration. The chief adulteration consists in the admixture of fish liver oil of lower quality or the use of blubber oil. Seal and whale oils have been used very extensively in the adulteration of cod liver oil. Japan fish oil and, in fact, all other fish oils which are of a character not to disguise the properties of cod liver oil have been used. It is evident that it is with extreme difficulty that the presence of these adulterants can be detected, especially if they are used in small quantities. The only certain method of guarantee of the purity of a cod liver oil is in the proper inspection and control of the manufacturing works. The livers of many other kinds of fish are employed in the manufacture of cod liver oil, but the other varieties have little value as compared with the cod liver oil itself and they are probably used almost exclusively in the adulteration of the genuine article. The Norwegian cod fish gives a much better character of oil than those coming from the Atlantic coast of America. In fact the latter product is of little medicinal food value and is used chiefly in the leather trade. =Blubber Oil.=--Blubber oil includes the oils made from seals, whales, turtles, etc., and is used exclusively for technical purposes, unless surreptitiously placed in cod liver oil as an adulterant. PART IV. MILK AND MILK PRODUCTS AND OLEOMARGARINE. MILK. =Limitation of Name.=--By the term “milk,” unless qualified in some way, is meant a lacteal secretion of the healthy cow, free of colostrum and of standard quality. If the milk of other mammals is meant the name of the class of animal is used in connection with the term, such as ewe’s milk, goat’s milk, etc. Milk is one of the most important articles of commerce and, by reason of its composition, high nutritive character, and easy digestibility, it is not only the natural food of infants but a most important food for children and adults. It is also an indispensable food in many, if not most, cases of disease where nutrition is impaired. In some cases life may often be sustained over a critical period by the use of milk as a food where other forms of food would fail of digestion and prove injurious instead of beneficial. The United States standard for milk is found in Appendix A.