There is a very general opinion that susceptibility to infections depends largely upon the nutrition and vital strength of the system irrespective of any tendency to the conveyance of disease germs by the habits of the individual in regard to diet or other details. A critical consideration of the subject, taking each infectious disease seriatim, has led the author to the belief that there is absolutely no foundation for this opinion, excepting in regard to tuberculosis.

Any parasite, including pathogenic bacteria, may be conveyed by any medium which is not lethal to the parasite. Hence, practically every parasite, using the word in the broadest sense, may occasionally be conveyed by food or drink.

Only two common infections are characteristically conveyed by water - typhoid and cholera - but probably non-specific choleraic diseases, dysentery and various infections of rather limited geographic distribution are also water-borne. Milk and ice and, to a less degree, various food stuffs, especially those eaten raw, may be contaminated through the use of water. In the case of milk, the water may be an adulterant, or infected water may have been used to wash the containers. When typhoid occurs in the family of a milkman, gross contamination may occur in various ways, as by high degree of contamination of water supply, contact of udders with faeces thrown onto manure heaps, infection of milk by the unwashed hands of attendants on patients, etc. Oysters, clams, etc., are often purposely grown near outlets of sewers and, hence, if eaten raw, may transmit typhoid.

Ice, though undoubtedly a means of conveying typhoid, since the bacilli are not immediately killed by freezing, is not an important means, for even a few days' freezing reduces the bacilli almost as much as sand filtration of water. In the course of four or five weeks, especially if alternate freezing and thawing have occured, very few bacilli are left alive, even if the original contamination has been excessive. Thus a very efficient and oeconomic means of preventing typhoid infection through ice, is the insist-ance on the use of old ice first.

In the case of patients with any contagious disease, even including tuberculosis and, for the sake of being on the safe side, malignant and other diseases not positively known to be infectious, care should be taken against the conveyance of germs by food remnants, eating utensils, etc., destruction of food remnants by fire being advisable in most cases. Attendants should never eat or drink in the sick room and should wash and disinfect the hands before eating or drinking.

Diphtheria, syphilis, tuberculosis, leprosy and various local septic processes, are liable to be conveyed by public drinking cups and imperfectly washed table utensils.

Various habitual entozoa as the gregarines, monads, cermonas, trichomoas, infusoria, rotifera and cyclops, of not much pathogenic importance, are commonly introduced in drinking water and fresh vegetables.

The amoeba - many distinguish A. coli, not markedly pathogenic, from A. dysenteriae, the cause of one form of dysentery - coccidium oviforme, balantidium coli and B. minutum, nycto-therus faba and megastoma entericum, are supposed to be introduced mainly from contaminated water and aquatic plants.

Certain trematodes are found as habitual parasites of wild fowl and are occasionally eaten as delicacies, being popularly supposed to be part of the fowl. Many of the rarer entozoa and those which penetrate to the deeper tissues, have a more or less complicated life cycle, either of the individual or of series of generations. In such instances, one stage of existence is liable to be "free living," in water or upon aquatic plants, so that introduction with food and drink is possible.

With this exception, and that of the cestodes (tape worms) and the trichina of the nematodes, the entozoa are not usually introduced by means of food and drink, except by purely accidental infection. The ascarides and oxyuris, trichocephalus, etc., are essentially what may be termed cheirophoric, that is to say, they are introduced by unclean hands. In the tropics, ova are frequently found beneath the finger nails. Children are especially liable to infection with this group of parasites on account of their close association with domestic animals, lack of aesthetic conceptions, and their proneness to live as close as possible to the floor or ground. Fresh vegetables and surface water are, however, very liable to be contaminated with ova from manure, including human excrement.

In certain of the cestodes, we have a distinct alternation of generations, the adult being an intestinal parasite of one animal, the ova accidentally swallowed by another, developing into a larval stage encysted in muscle and other deep tissues. Being eaten in the flesh, the larvae develop into adult worms in the intestine of the consuming host. While the same individual animal or species, may harbor the same worm in both adult and larval stages, at the same or different times, there is, in certain cases, a quite distinct succession of hosts of different species, for the respective stages of life of the parasite.

Taenia solium occurs in the larval or cysticercal stage in measly pork and when eaten by man, develops the corresponding tape worm. An exactly analogous process occurs for taenia sag-inata of beef. The corresponding cysticercal stages in man are rare.

Taenia nana occurs only in the adult form in man, the intermediary host being supposed to be an insect or snail, but it has not been connected with the edible snail, or with any other food stuff.

Taenia elliptica or cucumerina is more common in the dog and cat than in man; it is usually harmless, does not - unless very rarely - infest man or the domestic animals in the cysticercal -stage and is not connected with diet. Its intermediary host is supposed to be a louse or flea.

Taenia ecchinococcus occurs in the adult form in the dog's intestine, infecting man and other animals in the cysticercal stage. Its transfer is, obviously, not connected with diet unless adventitiously.

Bothriocephalus latus, cordatus and crispus, have their larval stage in fish and are not yet known in this country except by direct importation from the Baltic. Swiss lakes and other regions of north-western Europe. Their transfer to man, in the adult stage of intestinal parasites is exactly analogous to that of T. solium and T. saginata.

Bothriocephalus liguloides occurs in man only in the larval stage.

Trichina spiralis, though not manifesting the alternate stages of the cestodes, is introduced in the same way as the taenia solium, by the ingestion of infected pork.

Anchylostomum or uncinaria duodenale (-is) and americanum (-a) occur in earth-workers and are endemic in certain localities, mainly of a sandy soil. They are often ascribed, especially in the anaemic cases of the southern America "crackers," to clay eating and doubtless are also introduced accidentally by food. The larvae, however, have been prove I to pass through the unbroken skin.

Tetanus, anthrax, equinia and malignant oedema, though usually introduced through large or minute wounds of the skin and upper mucous membranes, may occur through alimentary infection of a more or less accidental character. Intestinal anthrax is well known clinically in this form. Whether actual lesion of the alimentary mucous membrane is necessary, is not known. Tetanus is pretty positively shown to correspond in distribution to that of the horse, the bacilli being almost invariably present in the intestine of the horse and in all soil upon which horse manure is deposited. Thus, for civilized man, potential tetanus infection is ubiquitous and may be transmitted by a variety of ways but, fortunately, the germs do not cause trouble unless introduced in such a way as to grow anaerobically.

Actinomycosis - two varieties of the fungus are recognized by many authorities - is due to a parasite of cereal plants and may develop, especially if a carious tooth or other lesion of the mouth or throat affords a portal of entry, from chewing wheat, or the habit of holding grass or straw in the mouth, or may be disseminated by dust from grain.

Bacillus aerogenes capsulatus infection is, by some, attributed to introduction of the germs in food.

Foot and mouth diseases may be transmitted by milk, especially to children, otherwise, the only infection likely to be transmitted by foods, except in an entirely adventitious and occasional way, is tuberculosis. The bacillus tuberculosis seems to have evolved from the hay bacillus, as a pathogenic parasite of cattle and to have been modified into a fairly distinct variety for human beings. According to the hygienic conditions under which cattle live, the incidence of bovine tuberculosis varies from practically nothing up to nearly 100% for certain small herds subjected to prolonged opportunities for infection from fomites and direct association.

Sheep and goats are nearly immune to tuberculosis and while horses and swine may be infected, bovine animals and particularly domestic cattle are the only important source of infection to man.

While tubercular diseases are described for birds and even cold blooded animals, these seem to have no immediate relation to tuberculosis as the term is ordinarily, specifically, employed and not to be transmissible to man.

Koch and some of his adherents have claimed that the difference between the human and the bovine tubercle bacillus is so well established that mutual infection is impossible. This claim has, however, been disproved by the most convincing experiments and clinical observations, bearing upon the transmissibility in both directions. However, it must be admitted that the two strains of tubercle bacilli have become pretty distinct and that mutual infection is not frequent. There is very plausible evidence that ordinary consumption is due to the human variety, while glandular and osseous tuberculous is mainly or entirely due to the bovine tubercle bacillus. If this is the case, the majority of cases of tuberculosis in human beings are mainly of respiratory or traumatic implantation, while mesenteric, osseous, and miliary and allied forms are mainly ingestive and due to tuberculous meat or milk.

Tuberculosis of food origin is, therefore, more common in infants but some authorities claim - apparently without good grounds, - that the most frequent portal of entry for all tuberculosis is the alimentary tract, especially the tonsils and intestinal lymph tissue and that the disease may remain latent for long periods, even of many years.