1. Outbreaks of mild food poisoning have been investigated in which heat-resistant Cl. welchii appeared to be the causative organism. The outbreaks were characterized by colic and diarrhoea without vomiting, commencing 8–20 hr. after ingestion of the contaminated food.
2. The strains of Cl. welchii concerned are only feebly toxigenic, and apart from the heat-resistance of their spores, and some colonial characters, fit well into Cl. welchii Type A. The toxin production and the serology of the strains is uniform within an outbreak.
3. Mild food poisoning similar to that seen in natural epidemics has been produced in volunteers by ingestion of cultures of heat-resistant Cl. welchii isolated from contaminated meat.
4. Infection is almost invariably due to meat which has been boiled, steamed, braised, stewed or insufficiently roasted, allowed to cool slowly, and eaten the next day, either cold or reheated.
5. Outbreaks of this kind should be prevented by cooking meat immediately before consumption; or, if this is impossible, by cooling the cooked meat rapidly and keeping it refrigerated until it is required for use.