antidotes of each other, and we know that they are not taken indiscriminately, although in a chief action they are interchangeable.

Coffee also has been said to lessen metamorphosis of animal tissues, because the emission of urea was lessened, but this implies that urea is a measure of tissue change, which cannot now be supported by facts. This introduces one of the most interesting discoveries of the day, in which my own researches have led the way by showing that the emission of carbonic acid by the lungs is the true measure of muscular exertion. I proved in my paper in the 'Phil. Trans.' for 1859, that even the movement of the hand could be measured by that standard; whilst in my paper in the Phil. Trans.' for 1862, I showed that the violent exertion of the treadwheel caused scarcely an appreciable increase in the emission of urea, and supported the results simultaneously obtained by Bischoff and Voit in experiments on dogs.

The discussion of this subject will be more fittingly pursued in the work on Dietaries; and I shall here be content with simply indicating the change of basis on which the estimation of muscular waste must now be made.

Coffee is an excitant of the nervous system, but not in the same degree as tea. It produces sleeplessness in many persons when it is taken at night, probably by exciting the heart's action, and preventing that fall which is natural at night, and requisite to permit sound sleep. I do not think that there is the same degree of reaction after taking strong coffee as follows strong tea. It is needless to add, that none of these effects may be marked if the infusion be very weak, as is common among the poor, and in this respect it resembles very weak tea.

Strong coffee is a valuable antidote in poisoning by

opium; and may be used as a corrective of the action of tea in persons whose skin is very active.

The addition of milk, which is so universal, forms a more perfect food with coffee than with tea; for both the former have the same kind of action on the skin and respiration, and therefore aid each other, whilst milk counteracts, in a degree, the action of tea upon the skin.

The addition of chicory to coffee does not increase its action upon any part of the system, but rather lessens it, and can be approved only as modifying the flavour of the coffee.

The adulterations of unground coffee are not nu

merous.

CHICORY.

Chicory (Cichorium intibus), with which coffee is, and has long been, mixed, both in this country and on the Continent, is the product of a compound plant growing in all European countries, and now cultivated largely for this purpose. It is said to have little property in common with coffee, and to be useful only by giving colour and a certain body to the infusion of coffee; but there can be no doubt that it possesses an aromatic oil, starch, sugar, nitrogenous substances, and salts; and, however inferior to coffee, the direction of the action of both is the same (No. 133).

We found in our experiments that half an ounce of chicory with 8 oz. of boiling water gave a maximum increase of 1.17 and 0.66 grain of carbonic acid, and 27 and 42 cubic inches of air inspired per minute, in ourself and friend, whilst the depth of inspiration was increased almost as much as from tea. Hence, it cannot be regarded as valueless, and indeed the price at which it is sold shows that it is appreciated as a food.

The root from which the powder is prepared is long

and tapering, and, after having been cut into pieces, is roasted with fat, precisely as coffee beans are roasted, until it is of a brown colour and sufficiently dry to be ground into powder.

It is said to be much adulterated with roasted rye, and with substances which sometimes yield a disagreeable smell and flavour.

COCOA AND CHOCOLATE.

These well-known substances are valuable foods, since they are not only allied to tea and coffee as respiratory excitants, but possess a large quantity of fat and other food materials.

Chocolate is produced from the seed of the cocoa palm (Cacao Theobroma), the pods of the ground nut (Arachis hypogaa), the cacao shrub of Zanzibar, and from other sources.

The seeds of the cacao are enclosed in a fruit somewhat like a cucumber in size, and are extracted by burying the fruit in the earth until the pulpy matter becomes rotten, or by first fermenting the fruit and then extracting the seeds by hand and drying them in the sun. They are about the size of an almond, and when broken into small pieces are subjected to great pressure until they are reduced to a rough powder, after which they are mixed with sugar and rolled into a very thick paste, or into a very fine powder, called Chocolate.

Cocoa nibs are the nuts roughly broken, and may be boiled in that state, but the mass is not so soluble as that which results from a more perfect system of preparation.

The peculiar active principle of cocoa and chocolate is the same, viz., theobromine, which resembles theine and caffeine, and has for its formula C7 H8 N1 02. There is also a very large proportion of oil or fat, which is the chief nutritive element.

The following is the analysis of the cacao bean from various localities by Tuchen (per cent.) :—

The fleshy part of the fruit is not used for the preparation of cocoa or chocolate, but is fermented and a vinous liquor made from it.

This substance in its action is less exciting to the nervous system than tea or coffee, and at the same time it contains a much larger proportion of nutritive material. Moreover, its flavour is not lessened by the addition of milk, so that it may be boiled in milk only, and thus produce a most agreeable and nutritious food. There are therefore many persons, states of system and circumstances, in which its use is to be preferred to either tea or coffee.

It is essential when using cocoa nibs to boil them for many hours in water, but the prepared cocoa or chocolate is soluble in boiling water.

So valuable a substance is liable to adulteration, and one of the most harmless is the admixture of starch or flour, but this may be readily detected by the form and figure of the starch (page 147).

We have already referred to the admixture of sugar with prepared cocoas, and with sugar at 31d. per lb., and

cocoa at more than twice that sum, the admixture far more than repays the cost of manufacture.

There are 3,934 grains of carbon and 140 grains of nitrogen in 1 lb. of unsweetened cocoa or chocolate.

CHAPTER XXXVI.

ALCOHOLS.

WE now approach the consideration of a class of substances usually regarded as foods, of perhaps greater importance in their effects upon a community than any other, and whilst they afford pleasure and health to some, give pleasure and disease to many, and both on the question of their right to be called foods and upon moral grounds, are driving civilised nations into two hostile camps.

It is impossible on any occasion, when these agents are considered, to omit all reference to moral effects, and scarcely possible to doubt that the abuse of them by so many does not more than overbalance the good produced on many more; but our space does not allow us to enter upon this branch of the subject, and, whilst entertaining strong views that a further limitation in their use would be a great advantage, we shall restrict our observations solely to the scientific and dietetic aspects of the subject.

It is first necessary to insist upon the facts, that alcohol does not represent alcohols, and that alcohols cannot be regarded as a homogeneous class of fluids because they have one element in common.

It seems strange that it should be necessary to insist upon the first statement, for with one element among many it is irrational to assume that it should give