When in addition it is taken into consideration that the ordinary roasting or broiling of a piece of meat is often not sufficient to produce a germicidal temperature throughout, the argument that a heat-resistant toxin is present in such cases is not conclusive. It must be remembered also that in some outbreaks those persons consuming raw or partly cooked meat have been affected while at the same time others eating well-cooked meat from the same animal have remained exempt; this would seem to indicate the destruction of living bacilli by heat, since the toxic substances formed by these organisms are heat-resistant. The view that a definite infection occurs, is favored, too, by the fact that the blood-serum of affected persons so frequently has an agglutinative action upon the paratyphoid bacillus. This would not be the case if the symptoms were due to toxic substances alone. Altogether the rôle of toxins formed by _B. enteritidis_ and its allies in food outside the body cannot be said to be established. The available evidence points to infection as the main, if not the sole, way in which the bacilli of this group are harmful. _Sources of infection._--The main sources of _enteritidis-suipestifer_ infection are: (1) diseased domestic animals, the infected flesh or milk of which is used for food; (2) infection of food by human carriers during the process of preparation or serving. To these may be added a third possibility: (3) contamination of food with bacteria of this group which are inhabitants of the normal animal intestine. Considering these in order: 1. Diseased animals: The majority of the meat poisoning outbreaks are caused by meat derived from pigs or cattle. Table III gives the figures for a number of British[77] and German[78] epidemics. TABLE III[79] ==================================================================== | | | BELONGING TO | B. ENTERITIDIS | B. SUIPESTIFER | THIS GROUP BUT | | |UNDIFFERENTIATED |--------------------+--------------------+---------------- |British|German|Total|British|German|Total| British ---------+-------+------+-----+-------+------+-----+---------------- Pig | 1 | 1 | 2 | 3 | 5 | 8 | 4 Ox or cow| 3 | 9 | 12 | 2 | 3 | 5 | 5 Calf | 0 | 7 | 7 | 2 | 2 | 4 | 0 Horse | 0 | 1 | 1 | 0 | 1 | 1 | ... Chickens | 1 | 0 | 1 | 0 | 1 | 1 | ... -------------------------------------------------------------------- Occasional outbreaks have also been attributed to infection through eating rabbit, sheep, goose, fish, shrimp, and oysters. Especially noteworthy is the relative rarity of infection from the meat of the sheep.