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"If the starch alone is to be determined, deduct seven from the factor and multiply the specific gravity by the number thus obtained; the result is the percentage of starch.

"If the specific gravity of the potato is below 1068, the quality is very bad; between 10681082, the quality is very inferior; between 1082-1105, the quality is rather poor; above 1105, the quality is very good; above 1110, the quality is best."

A poisonous principle, termed solanine, is said to become developed in the buds and shoots of potatoes that are allowed to grow out on keeping; but no case is recorded, notwithstanding the universal consumption, of poisonous effects arising from the use of such potatoes.

With regard to the cooking of potatoes, the best general method is, without doubt, either to bake or steam them in their skins. Dr. Letheby asserts that when potatoes are peeled and then boiled, the loss in cooking is 14 per cent.; but if cooked without peeling, it is only 3 per cent.

The Potato Disease. -In the United States in 1843 a disastrous disease appeared among the potato crops; in 1844 it had reached Canada, and before the end of 1855 it had shown itself in most European countries. Since that date this disease appears to have been on the increase, and it resists all efforts to eradicate it. It usually appears in July, August, September, and October, but a few crops have been attacked in May. A mild and moist atmosphere appears to favour the spread of this malady, and no soil is exempt from its attacks, though sloping well-drained soils are always the least affected. An abundance of manure, especially if directly applied, often corresponds with the maximum intensity of the plague; and again, the potatoes only lightly covered by the soil have frequently been those most violently attacked. No variety has been able to resist this disease, though one or two have in a measure succeeded in escaping its influence. It commences in the leaves of the plant, and thence extends from the stem to the tubers. On the surface of the latter brown spots make their appearance, penetrate the substance, and eventually lead to decay.

The disease is caused by a minute fungus called Peronospora infestans. The life-history,

a large portion of which has long been known by the researches of Montague, Berkeley, De Pary, and others, has recently been completed by the discoveries and investigations of Worthington G. Smith. Fig. 68, reduced from a cut in the "Gardeners' Chronicle" (July 17, 1875) to one of Mr. Smith's original papers, will give an idea of the nature and method of reproduction of the fungus. It represents & very fine and successful section of the leaf of a diseased potato highly magnified. A A are the minute hairs always present; B B are the individual cells of the leaf. The former are structures belonging entirely to the healthy plant, whilst the threads and bodies shown at C, D, E, F, and G belong to the fungus, the parasite which preys upon the plant. The fine thread at C is a continuation of the spawn or mycelium living inside, and at the expense of the assimilated material of the leaf. Emerging into the air, the thread ramifies at the tips of the branches and bears fruit, D D. These fruits are termed simple spores, or conidia, because of their dust-like appearance. The conidia are capable of germinating and reproducing the species just in the same way as a seed. A second method of reproduction of the peronospora is shown in the "swarm-spores " E F. These, when moistened artificially, or in nature by dew or rain, set free fifteen or sixteen bodies known as "zoospores," so named because they exhibit every phenomenon of animal and spermatozoa-like life. They are furnished with two lash-like tails, and move about for half an hour with great rapidity. The zoospores falling upon any portion of the plant, have an extraordinary power of instantly corroding and boring through the cellular epidermis. When movement ceases, the tails (cilia) disappear, the zoospores burst at one end, and protrude a tube which develops into mycelium, producing, as before, the perfect plant. These two asexual methods of reproduction have long been known, but as in both of them the structures are far too delicate to withstand the frosts of winter, it was dificult to account for its winter life until Mr. Sith showed that the third mode of reproduc tion, already made out in similar species of peronospora, was also to be found in the potato plant. The third form is a true sexual method, perfectly analogous to the reproduction of the higher flowering plants. This third method is the production of eggshaped bodies, about 15 of an inch in diameter, known as "oospores." The oospores are produced by the conjugation of two bodies the one, the male, known as the antheridium (see H, fig. 68), and analogous to the anther of a flower; and the other the

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SPECTION OF.

the diseased potato plants in the world were and if necessary seize, poultry. See FOOD, IN-
destroyed, in the next season the fungus
might again invade the crops from other sol-
anaceous plants.

Potato, Sweet-See BATATta.

Poultry - Poultry usually contains too much nitrogenous matter and too little fat to be very nourishing. The duck and the goose, which possess more fat, contain certain flavouring matters which are not easy of digestion. No bird nor bird's egg is known to be poisonous, but some birds are rendered poisonous by the food which they have eaten. The pheasant, for instance, which feeds on the buds of the Calmia latifolia, in North America, is deemed poisonous during the winter and spring; and birds in this country which have fed on poisoned grain have produced serious symptoms in those who have eaten them.

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Poverty-See PAUPERISM.

Powers of Sanitary AuthoritiesSee SANITARY AUTHORITIES.

Preserves - Preserved fruits-jams,

jellies, &c.-frequently contain copper, and in some cases this metal has been found to be present in large quantities. It is derived either from the copper vessels in which the preserves are often prepared, or has been added to improve the colour of the article. See COPPER.

Prevention of Disease - See EPIDEMIC, &c.

Prices-The prices of the principal pro visions have greatly increased since 1852. The following table clearly shows this:

A medical officer of health, &c., may inspect,
The AVERAGE PRICES of CONSOLS, of WHEAT, of MEAT, and of POTATOES in each of the
Twenty Years 1852-1871.

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ventilated, and have walls perfectly watertight. The forms of privies are innumerable: the simplest is perhaps a galvanised zinc pan,

Fig. 72

either furnished with handles or on wheels, and put close up to an ordinary seat: this is emptied when necessary.

Fig. 71.

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The lid of refuse-bin to be of best 1-in. red deal boards, with two strong ledges or battens across them; to be hung with three strong band hinges to the sides of the ventilating-shafts, and the making. up piece between the same. A circular orifice to be made in centre of lid, between the battens, 10 in. wide. The lid to have two coats of boiled tar both inside and out.

A 4 and 3 in. frame, of red deal, to be securely fixed on top of the dust-bin as a seat for the lid.

A lid over the privy seat to be hinged on 'at the back, with a child's seat over centre of large one. The larger seat to be provided with an earthenware circular rim beneath.

The earth compartment to be without lid, and provided with a pint scope for each occupant to throw in a pint of the stored dry earth or dry ashes through the seat into the galvanised iron pail, the contents of which must be scattered over the garden, or put in the dust-bin, before the pail becomes full. A loose foot-block may be furnished where there are young

children.

The dust-bin may be placed at side of the privy if required. The floor of dust-bin to be at the groundlevel, slightly inclined outwards, and paved with brick.* (Figs. 69-72.)

The chief provisions as to privies and closets are as follows :

:

It is not lawful newly to erect any house, or to rebuild any house pulled down to or below the ground-floor, without a sufficient watercloset, earth-closet, or privy, and an ashpit, furnished with proper doors and coverings. Penalty for contravention, £20 or less.-(P. H., s. 35.)

If a house within the district of a local authority appears to such authority by the report of their surveyor or inspector of nuisances to be without a sufficient water-closet,

earth-closet, or privy, and an ashpit, furnished with proper doors and coverings, the local authority shall, by written notice, require the owner or occupier of the house, within a reasonable time therein specified, to provide a sufficient water-closet, earth-closet, or privy, and an ashpit, furnished as aforesaid, or either

of them, as the case may require.

If such notice is not complied with, the local authority may, at the expiration of the time specified in the notice, do the work required, and may recover in a summary man

*The above forms can be obtained of Knight & Co., 90 Fleet Street, London,

ner from the owner the expenses incurred by them in so doing, or may by order declare the same to be private improvement expenses: provided that where a water-closet, earthcloset, or privy has been and is used in common by the inmates of two or more houses, or if in the opinion of the local authority a water-closet, earth-closet, or privy, may be so used, they need not require the same to be provided for each house.-(P. H., s. 36.)

Any enactment in force within the district of any local authority requiring the construction of a water-closet shall be deemed to be satisfied by the construction, with the approval of the local authority, of an earth-closet.

Any local authority may, as respects any house in which any earth-closet is in use with their approval, dispense with the supply of water required by any contract or enactment to be furnished to any water-closet in such house, on such terms as may be agreed on between such authority and the person providing or required to provide such supply of

water.

Any local authority may themselves undertake or contract with any person to undertake a supply of dry earth or other deodorising substance to any house within their district for the purpose of any earth-closet.

The term "earth-closet" is to include any place for the reception and deodorisation of fæcal matter constructed to the satisfaction of the local authority-(P. H., s. 37.) See also CLOSETS, FACTORIES, NUISANCES, PUBLIC NECESSARIES, SCAVENGING.

Prostitution-The prevention of this terrible evil has baffled the united efforts of hygienist. Prostitutes have existed from the the legislator, the philanthropist, and the

most ancient times down to our own, and so

long as human nature is the same as it is now will continue to exist. The only practical means of in any way controlling this vice within bounds is to render clandestine prostitution impossible, to register public, and to their manner of life, as well as by periodical give prostitutes every facility of reforming inspection to be able to isolate and cure those who are affected by venereal disease, and thus prevent its propagation.

tutes, except in those few places where the It is difficult to know the number of prostiContagious Diseases Acts are in force. In London, for example, only the more notoric 23 and it is evident that clandestine prostitute, and open prostitutes are known to the police; which is known to exist to a considers de amount, will always render official returns inaccurate. The following table, however, gives some idea of London prostitution:

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