name given by Selmi to certain basic compounds formed in the later stages of protein disintegration. Interest in the ptomains was especially stimulated by the work of Brieger, who isolated and stuided (1882-1888) the properties of many of these bodies.

Confidence in the sanitary significance of ptomains has been shaken by many facts. For one thing, ptomains are formed in the later stages of protein decomposition, and by the time they are present, the organoleptic evidences of decomposition have become pronounced. There is little doubt that food containing ptomains would be almost invariably condemned by the senses as nauseating and unfit for use. On technical grounds numerous criticisms have been made with respect to the methods used for isolating and extracting ptomains and for determining their clinical effect. Perhaps the principal reason, however, for the decline in the belief that ptomains have any important share in the production of food poisoning has been the discovery that in many instances the responsibility can be placed definitely upon other factors. Those outbreaks of food poisoning that have been most thoroughly investigated have been found to be due not to the use of spoiled food containing ptomains but either (1) to the presence of true bacterial toxins comparable to the toxins of the diphtheria and tetanus bacilli and not to be regarded as the simple products of decomposition, or (2) to infection with specific bacteria borne in or upon the implicated food article.

Poisoning from bacterial products in food, when it occurs at all, seems to be due to the accidental and occasional presence of toxigenic microbes which give rise to specific toxins. Little is known about the conditions under which the relatively rare toxigenic bacteria find their way into food

stuffs. In the best-known example of this type, the severe poisoning due to the products of Bacillus botulinus, certain facts seem to indicate a regional distribution of the microorganisms. In this country 17 of the 22 recorded outbreaks have occurred in California. There is no record of a single case in Great Britain. All told, demonstrated instances of food poisoning due to bacterial products are not very nu

merous.

On the other hand, the careful investigation of food-poisoning outbreaks has brought to light a very large number of instances of apparent poisoning which are in reality cases of infection with some pathogenic microorganism. The distinction is practically important. The measures that need to be taken to prevent infection are of a different nature from those designed to prevent the use of food containing the products of bacterial growth.

There are still many questions about the use of spoiled foods that need settlement. Some foods such as cheese and sour milk that are loaded with the products of microbic activity appear to be used with impunity, but while we are not yet able to specify with precision the differences between harmful and harmless bacterial action, there can be little doubt that the almost universal preference for fresh food containing as few bacteria as possible rests on a sound physiological basis.

Food-borne infections are essentially of two separate and quite independent classes:

2 A number of obscure points in botulism intoxication remain to be cleared up. The discoverer and leading student of the biology of the botulism bacillus, Van Ermengem, states that the spores are destroyed by 15 minutes' heating at 85° (185° F.) or by 30 minutes' at 80° (176° F.), but Dickson (Jour. Amer. Med. Association, 1917, 69, p. 966) has recently reported observations indicating much greater heat resistance. Further investigation of this important question is urgently needed.

those in which the pathogenic organisms are present in the food at its origin, without human intervention; and those in which the food has become contaminated from human sources during the process of preparation, transportation or serving.

The contamination of food with disease germs on its way from source to consumer may occur through direct contact either with a person suffering from disease or a convalescent or a healthy carrier. From such an individual the specific pathogens may be conveyed to the food by mouthspray or by contaminated fingers.

It probably does not often happen that such contamination is brought about by a person seriously ill with a specific infection except in the initial or later stages of the malady. The incapacitating effects of most infectious diseases tend to prevent the active participation of the patient in marketing or serving food. Mild or atypical cases, however, of such diseases as typhoid fever are a source of danger, and instances are on record where food-borne infections have originated from definitely affected persons. From the public-health standpoint infection from this source is important and must be guarded against with great vigilance.

In a variety of human infections convalescents constitute an important source of food contamination. As is well known, pathogenic organisms may be present in the nose or throat, in the intestines or in other organs, for some time after clinical recovery has taken place. It is possible in diphtheria and some other infections to determine with a high degree of certainty when the specific germs finally disappear from the body, but unfortunately this knowledge is not always taken advantage of in actual practise. There is reason to believe that in typhoid fever, for instance, patients frequently are released

from the hospital while they are still discharging typhoid bacilli from the bowels. or bladder. The hospital authorities often do not inform their clients or themselves on this point, and the germ-bearing convalescent is not warned of the danger to family and associates which his condition involves. In some infections the length of persistence of the specific germs can not be determined by present methods, and consequently only rule-of-thumb methods of quarantine are practicable. As matters stand, it is plain that food-handling by those recently convalescent from any infectious disease is always to be avoided; knowledge of this fact should be spread as widely as possible.

It is not necessary to dwell at length on the significance of the true "carrier" in food-borne infections, since in recent years the nature of the disease-carrier problem has been given wide publicity. The term disease carrier is commonly applied to those in whom the specific germ persists far beyond the usual period of convalescence and also to those who harbor a disease-producing microbe, although they have apparently never suffered from a clinical attack. It is evident that this latter group constitutes a peculiarly insidious source of infection, since the possession of disease-conveying power is often entirely unsuspected by the persons affected, and is only revealed by investigations following an actual outbreak. The majority of the

8 A remarkable instance of a typhoid carrier has been reported by Jundell (Hygiea, Festband, 1908; editorial, Jour. Amer. Med. Assoc., 1909, 52, p. 388). The grandmother, 79 years old, of a large family was found in 1908 to harbor typhoid bacilli and had apparently been responsible in her lifetime for some thirty-two cases of typhoid fever in members of her family and in servants and other persons in the household. The period during which this carrier was capable of conveying infection apparently extended over fifty-four years,

"healthy carriers," however, are known to have been recently in contact with patients or convalescents.

Efforts to keep down the number of food-borne infections due to the contamination of food by sick persons, convalescents or carriers are therefore mainly directed to placing the ordinary food manipulations in the hands of healthy persons and of those who have not been recently in contact with the sick. This task is somewhat simplified by the rather limited number of diseases likely to be conveyed through such agencies. The chief food-borne infections hitherto traced to human contamination are typhoid fever and the various paratyphoid infections.

To these must

be added certain infections transmitted in milk which are rarely, if ever, conveyed in other food-stuffs. Outbreaks of diphtheria, scarlet fever and streptococcus sore throat due to milk have been reported in considerable numbers, but foods other than milk probably seldom serve as the vehicle of these diseases. In the majority, if not in all, of these cases, the specific germ enters the milk directly from human sources. It is probable, however, that in some instances a secondarily infected cow must be held responsible. It is theoretically possible for the bacillus of human tuberculosis to be transmitted by food, but evidence of the frequency of such transmission is not readily forthcoming. Even the contamination of milk by a tuberculous milker is not easy to prove. Since it is almost impossible to trace most cases of tuberculosis to their origin, any precise evaluation of source of infection in this disease is at present out of the question. Technical difficulties, however, should not be allowed to override the application of ana1854-1908. The disease was confined strictly to this one family, and the neighborhood was free from typhoid fever during all these years.

logies drawn from other diseases. It seems entirely reasonable to suppose that milk and other foods can become contaminated in the course of their collection or handling by a person discharging human tubercle bacilli. In the recent examination in New York City of 1980 food-handlers, 10 cases of active tuberculosis were found. The agency of flies in bringing about the contamination of food both with tubercle and typhoid bacilli must also be taken into consideration.

It can not be forgotten that there is a possibility of the multiplication of pathogenic bacteria in food. In general, microorganisms pathogenic for man do not increase freely outside the human body, and when discharged into the air, water or soil, quickly perish. But in many foods. conditions obtain very much like those in the artificial culture media used in laboratories. If such foods become contaminated with pathogenic bacteria, a considerable increase in bacterial numbers may occur. In point of fact, it has been observed that multiplication of this sort does take place. There are many instances where the incriminated food, when fresh, gave rise to little or no injury, but after standing 24 hours or less without visible signs. of decomposition produced numerous cases of illness. Especially significant is the large number of outbreaks in which such foods as meat jellies, meat pies, salads and made dishes generally have been inculpated. A very large proportion of the recorded outbreaks has been traced to foods that have been prepared for the table and then allowed to stand before being eaten, or that have kept over to a second or third day as remnants after the first serving. Cooking, so far from surely destroying all bacteria, may in some cases provide a favorable temperature for bacterial multiplication, as in the celebrated California

outbreak of 93 cases of typhoid infection due to a dish of baked spaghetti. Here it was found by subsequent experiment that the degree of heat reached in the interior of the dish was an incubating rather than a sterilizing temperature. Milk, which is an excellent culture medium, is a food particularly liable to become dangerous through the multiplication of bacteria. The mixing of milk from many farms at a central station tends to disseminate any contamination present through the whole supply. One typhoid carrier on a single farm may therefore lead to the contamination of a large volume of raw milk and to an extensive epidemic. The pasteurization of milk offers a satisfactory method of meeting this danger.

Besides the various modes of direct contact there are more roundabout methods of food contamination from human sources of infection. One possibility is the transmission of typhoid infection by vegetables grown on land fertilized by night soil. The practise of manuring truck gardens with human excreta is not unknown in this country and is believed by some to be increasing. Melick has shown that typhoid bacilli may remain attached for several weeks to lettuce and radishes grown in contaminated soil, a period quite sufficient for the maturing of these vegetables. He also showed that the bacilli are not removed from the surfaces of the vegetables by the ordinary methods of washing used in preparing such foods for the table.

The second type of food-borne infection, that in which the food itself is contaminated at its origin and does not simply pick up contamination en route to the consumer, is especially exemplified in the case of certain infections of the ordinary food animals. Food plants are not attacked by any microorganism pathogenic to man, with 4 Jour. Infect. Dis., 1917, 21, p. 28.

perhaps the single exception of the coconut palm, in which a disease called bud-rot is said to be caused by a variety of B. coli, an organism usually harmless but under some conditions slightly pathogenic for man. The rather numerous species of bacteria that cause the diseases to which the common garden vegetables are subject are none of them, so far as known, pathogenic for man or other animals. On the other hand, many food animals suffer from bacterial infections that may be communicated to man.

Milk is probably the animal food that serves most commonly as the vehicle of this type of infection. It has been definitely established that the bacillus of bovine tuberculosis may be present in the milk of a diseased cow and that the use of such milk in a raw state is a source of human infection, particularly in young children. Milk from diseased animals may also produce infection in foot-and-mouth disease, in Malta fever (goat's milk) and in some other diseases. In many cases the condition of the animal is such as to give ample warning, in others the danger is not so readily apparent. Adequate pasteurization of the milk is a safeguard against this mode of infection as well as against infection with milk contaminated from hu

man sources.

Other food products originating from diseased animals may contain pathogenic bacteria. A noteworthy number of outbreaks of meat poisoning have been traced to the use of meat from animals ailing at the time they were slaughtered, and later discovered to have been definitely infected. Bacilli of the paratyphoid-enteritidis group are found in a large proportion of these cases, both in the meat of the diseased animals and in the organs or excreta of the persons affected. This class of food infections is of special interest, since in their

sudden onset and acute gastro-intestinal symptoms they present the characteristic features of what is popularly supposed to be ptomain poisoning. They are in reality genuine infections with pathogenic bacilli. Cattle and swine are apparently particularly prone to infection with bacteria of this group, and by far the larger number of meat-poisoning epidemics are due to meat from these animals. The meat of sheep is rarely implicated. It is noteworthy also that a large proportion of the recorded meat poisoning outbreaks are due to raw or imperfectly cooked dishes. Sausages, especially such as are made of raw meat and eaten without cooking, have been incriminated in a significantly large number of cases. Internal organs like the liver and kidneys are more apt to contain bacteria than the masses of muscle commonly eaten as "meat." Unfortunately, inspection of the meat may not give any warning of the presence of pathogenic bacteria. Meat in appearance quite normal to the trained eye of the veterinary has been known to give rise to a meat poisoning outbreak. Neither is it always practicable by a system of live-animal inspection to prevent the marketing of meat from infected animals. Thorough cooking is probably the best means of preventing this as well as all other forms of food-borne infection. While paratyphoid seems to be the most common form of meat-borne infection, there is a possibility that other kinds of pathogenic bacteria present in the bodies of diseased food animals may sometimes be transmitted to man in meat or meat products. The possible conveyance of tuberculosis in this way has been thoroughly investigated, and it is now pretty generally agreed that in most civilized countries the danger of contracting tuberculosis from meat is not serious. Under any ordinarily careful system of inspection tubercle-infected car

casses are not likely to be marketed without restriction, and the thorough cooking to which meat is commonly subjected is a further and efficient safeguard. It is apparently true also that very large numbers of tubercle bacilli are necessary to produce infection of human adults through the alimentary tract. Altogether the concurrence of favorable conditions for the transmission of tuberculosis by meat is probably rare. Bacilli of the "bovine" type are seldom found in adults. Although theoretically possible, there does not seem to be any convincing evidence that cases of tuberculosis have actually resulted from the use of meat.

In several acute diseases of food animals caused by bacilli pathogenic for man the possibility of human cases being food-borne is even more remote than in tuberculosis. Anthrax is not at all likely to be transmitted through food. Many diseases, such as hog cholera, swine erysipelas and pleuropneumonia of cattle that affect various domestic animals are not known to be transmissible to man in any way. Conversely, typhoid fever and Asiatic cholera are not diseases from which the lower animals suffer, and consequently are not infections that can originate with any food animal.

The chief infections therefore that are known to be due to food infected at its source are those mainly meat-bornecaused by the group of paratyphoid-enteritidis bacteria and those resulting from the use of infected milk. The methods for preventing food infection are not those of simple inspection of food products. It has been questioned whether the amount of disease prevented by the ordinary methods of food inspection is at all commensurate with the outlay. Chapin in considering the

5The Relative Values of Public Health Procedure," Jour. Amer. Med. Assoc., July 14, 1917, 69, p. 90.

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