Cases of poisoning by articles of food may be distinguished as: (1) those caused by some injurious constituent in the food itself, and (2) those caused by a peculiar condition of the individual consuming the food, by virtue of which essentially wholesome food substances are capable of producing physiological disturbance in certain individuals. The latter group includes persons, apparently normal in other respects, who are more or less injuriously affected by some particular article of diet, such as eggs or milk, which is eaten with impunity by all normal individuals. This is the so-called food sensitization or food allergy. Food poisoning, as more commonly understood, is due to the composition, contents, or contamination of the food itself. It is not within the scope of this book to consider any of those cases in which definite poisonous substances are added to food with criminal intent. The term food poisoning is here taken to include the occasional cases of poisoning from organic poisons present in normal animal or plant tissues, the more or less injurious consequences following the consumption of food into which formed mineral or organic poisons have been introduced by accident or with intent to improve appearances or keeping quality, the cases of infection due to the swallowing of bacteria and other parasites which infest or contaminate certain foods, and the poisoning due to deleterious substances produced in food by the growth of bacteria, molds, and similar organisms. As already pointed out, little is known about the relative frequency of occurrence of these different causes or the extent to which they are separately and collectively operative. THE ARTICLES OF FOOD MOST COMMONLY CONNECTED WITH FOOD POISONING In addition to the definitely poisonous plants or animals, certain everyday articles of food have been frequently associated with the more serious outbreaks of food poisoning. Meat in particular has been implicated so often that the term meat poisoning is used about as commonly as the term food poisoning in general discussions of this subject. Certain it is that the great majority of the best-studied and most severe outbreaks of food poisoning have been attributed on good grounds to the use of meat or meat products. Other animal foods, and especially milk and its derivatives, cheese and ice-cream, have likewise been held responsible for extensive and notable outbreaks. Perhaps the most significant feature of food poisoning attacks is the frequency with which they have been traced to the use of raw or imperfectly cooked food. The probable interpretation of this fact will be discussed in the later chapters. Especially have the use of uncooked milk, either by itself or mixed with other food substances, and the eating of raw sausage brought in their train symptoms of poisoning in a disproportionately large number of cases.