Compared with 20, or even 10, years ago our present knowledge of food poisoning outbreaks is extensive and in certain directions fairly complete. In spite of this greatly extended knowledge there are some aspects in regard to which we are yet lacking in fundamental information. This is particularly the case as to the precise sources of infection. It may be accepted as a demonstrated fact that most outbreaks of food poisoning are due to infection of the food eaten with one or other member of the Gaertner group of bacilli. The present paper is only concerned with the outbreaks associated with this group of organisms. A study of the individual outbreaks usually supplies evidence which definitely incriminates a certain article of food, and for most of the recent outbreaks further evidence is forthcoming that this has been infected with one or other member of the Gaertner group of bacilli. Tracing the matter a step further back it is only in a quite small minority of outbreaks that the recorded facts show how the food has become so infected. In a proportion of cases, perhaps more than half for continental recorded outbreaks but in only a small fraction of the British outbreaks, it is true that definite evidence is forthcoming showing that the meat was derived from an animal itself suffering from general or local disease caused by Gaertner group bacilli. Even, however, for these cases our recorded knowledge ceases with this information, and we do not know how these animals became infected or whether they represent isolated cases or are part of widespread epidemics amongst the animals affected.