Thus diet may be an actual cause of disease. Excess of protein material in Europeans, and deficiency of proteins in the poorer classes of natives and in some institutions, are instances of this.
A Native Prison Dietary , in use in one of the crown colonies, on which, as regards physical conditions, health may be maintained with little or no loss of weight, will serve to illustrate some of the points above referred to :
Ordinary diet .
Certain special articles of food are at times causes of definite diseases. Pellagra is reputed to be closely associated with the consumption of Indian corn, maize, in a diseased condition, especially when affected by fungi such as aspergillus fumigatus. Lathyrism is produced by the continued use of Lathyrus sativus and possibly of L. clymenum and cicera. Possibly rice in some of its forms may contain the poison of beri-beri. Ergotism occurs in the tropics as well as in temperate climates.
Certain articles in common consumption are at times poisonous, or may be so if insufficiently cooked. Cassava-manioc (Mainhot utilissima) contains a glucoside which in the presence of acids breaks up, setting free hydrocyanic acid. The amount of this glucoside varies with the age of the tuber, and also in different varieties of the plant. In the bitter cassava the amount is considerable, and if the root be eaten only partially cooked, fatal prussic acid poisoning may rapidly occur. Boiling breaks up the glucoside and prolonged boiling expels so much of the hydrocyanic acid that no poisonous effects will be produced. Cassa-reep, which forms the basis of so many sauces, is obtained by pressing the juice from the bitter cassava and allowing complete fermentation to take place whilst the juice is exposed to the air. If not properly mature a poisonous amount of prussic acid may be contained in this substance, though when fully mature it has all been destroyed.
Articles of food may be contaminated by flies with the organisms of various diseases. Flies are under some circumstances very prevalent and active in the tropics, and as human excreta are less thoroughly dealt with there, these insects are an important factor in the spread of disease. Cholera, as well as typhoid fever, has been shown to be carried in this manner. Cold meats therefore, are dangerous foods, for it may well be that they get contaminated by flies or other insects after they have been cooked and have cooled. Rats, again, may contaminate food with the plague bacillus.
Tinned Foods are extensively consumed in some tropical countries. They are frequently more used than they should be as, at the best, their nutritive value is less than that of fresh meat; moreover there is some risk of metallic poisoning. The most serious objection to the indiscriminate use of tinned meats is that it is not always easy to determine whether or not any given tin has been stocked too long. Some of those sent abroad are already old, and others are kept too long in the tropics. The better class of firms do not stock tins very long, but sell off surplus stock to small traders, and so in the remoter districts where these small traders are principally to be found, only very old tins may be procurable. In some cases there is obvious evidence of decomposition, the formation of gas having caused the tin to be "blown," i.e. the concave end to be bulged out and convex. Frequently the vendor perforates and reboils such tins, subsequently soldering up the puncture made. The contents of tins showing two soldered points, therefore, should not be used for food. It is to be regretted that, with the exception of Australasian goods, the stamping of tins with the date of preparation is not compulsory. Ptomaine poisoning from stale tinned food is by no means rare.
The main articles of food used in the dietetic treatment of acute diseases are milk, broths, barley, arrowroot, rice, and oatmeal; to these may be added various proprietary articles such as bovril, Liebig's extract, Valentine's meat juice, and many kinds of malted foods.
In many tropical countries, such as West Africa, milk cannot be obtained except in a preserved form. In other countries, cows', goats' or buffalos' milk can be readily procured. The nutritive values of these vary.
Buffalos' milk is very rich in fat, there being nearly twice as much as in cows' milk; it is also richer in proteins though not so rich in lactose. It is less digestible, has a peculiar smell and flavour, and, as a rule, is not suited for invalids.
Goats' milk differs less from cows' milk; but as the goat is susceptible to Malta fever, and the Micrococcus melitensis is discharged in the milk of infected animals, it is better not to use the milk of these animals unless efficiently pasteurized or, better, well boiled.
Where cows' milk is available, it should be used in prefer-ence to preserved milk. In the tropics, unless milk can be consumed fresh from the cow, it must be boiled, and thus rendered slightly less digestible.
It is necessary to boil milk in the tropics because :
(1) Under tropical conditions the growth of organisms is so rapid that milk quickly turns sour.
(2) The natives frequently add water to the milk and are apt to be careless as regards the washing and scalding of the utensils used.
(3) The water used for such dilution and for washing utensils is usually drawn from shallow wells or pools liable to contamination. Inspection and regulation of the milk supplies in the tropics are very lax.
(4) Obvious impurities are strained off with old rags or articles of clothing actually in use.
(5) Cattle are often fed on garbage of all kinds.
The obvious plan for minimizing the necessity for boiling where the milk is intended for consumption by Europeans, or for use in hospital, is to keep cattle under the best possible sanitary conditions and to ensure that they are milked with due hygienic precautions. This must be done under European supervision.