Foot-and-mouth disease of cattle is transmissible to man through the milk of infected cattle, but this infection in man is not very common or as a rule very serious. So far as known, it is not communicated to man in any other way except through the use of uncooked milk.

Such cases of infection or "poisoning" by milk may be prevented, as already stated, by the exclusive use of heated milk. The possible occurrence of nutritional disturbances (e.g., scurvy) in a small proportion of the children fed on pasteurized or boiled milk is considered by many physicians to be easily remedied and to possess much less practical importance than the avoidance of infection.

POSSIBLE INFECTION WITH B. PROTEUS

One widely distributed organism known as Bacillus proteus has been several times held responsible for food poisoning outbreaks, but it is not yet certain how far this accusation is justified. B. proteus is related to B. coli, but most varieties do not ferment lactose and are much more actively proteolytic than the latter organism, as shown by their ability to liquefy gelatin and casein. Like B. coli, they form indol and ferment dextrose with gas production. Varieties of B. proteus are found widely distributed in decomposing organic matter of all sorts.

The evidence upon which this bacillus is regarded as the cause of food poisoning is not altogether convincing. The outbreak described by Pfuhl[60] is typical. Eighty-one soldiers in a garrison at Hanover were suddenly attacked with acute gastro-enteritis four to twelve hours after eating sausage meat. The meat was found to contain B. proteus in large numbers, although it was prepared with ordinary care and was entirely normal in appearance, taste, and smell. Rats and mice fed with the sausage became ill and B. proteus was isolated from the blood and internal organs. But these animals sometimes die when fed with quite normal meat, and B. proteus and other common intestinal bacteria are often isolated from the body after death. B. proteus, in fact, is found in many animal foods and in the apparently normal human intestine. Like B. coli, it frequently invades the internal organs after or shortly before death. Finding B. proteus in food or in the internal organs does not therefore constitute definite proof of any causal relationship. The evidence attributing other outbreaks to infection with B. proteus is similarly inconclusive.

It is equally uncertain whether the production of a poison in food by this species can in any degree be held responsible for meat poisoning. B. proteus is common enough in decomposing food material and under certain circumstances is known to generate substances that are toxic for man. It is possibly true that toxic substances are produced in the early stages of decomposition by this organism. In the opinion of Mandel[61] and others, if any injurious effect at all is to be attributed to B. proteus, it is in the nature of an intoxication and not an infection (see [chapter viii]). So far as the existing evidence goes, the question of the responsibility of this organism for food poisoning is still an open one.

[CHAPTER VI]

FOOD-BORNE PATHOGENIC BACTERIA (Continued)

PARATYPHOID INFECTION

The most characteristic examples of "food poisoning," popularly speaking, are those in which the symptoms appear shortly after eating and in which gastro-intestinal disturbances predominate. In the typical group-outbreaks of this sort all grades of severity are manifested, but as a rule recovery takes place. The great majority of such cases that have been investigated by modern bacteriological methods show the presence of bacilli belonging to the so-called paratyphoid group (B. paratyphosus or B. enteritidis). Especially is it true of meat poisoning epidemics that paratyphoid bacilli are found in causal relation with them. Hübener[62] enumerates forty-two meat poisoning outbreaks in Germany in which bacilli of this group were shown to be implicated, and Savage[63] gives a list of twenty-seven similar outbreaks in Great Britain. In the United States relatively few outbreaks of this character have been placed on record, but it cannot be assumed that this is due to their rarity, since no adequate investigation of food poisoning cases is generally carried out in our American communities.