Celluloses are divided into three classes, according to their behaviour with reagents: (1) those like cotton fibre, which offer a maximum resistance to hydrolytic action; (2) those usually called oxycelluloses, which are less resistant to hydrolysis; (3) those which are more easily hydrolised, with a formation of carbohydrates of low molecular weight. The cellulose of the walls of the cells of seeds is an example of this class, and it is easily decomposed by acid and more or less soluble in alkalis. Allied bodies called pectins may be obtained from the juices of many fruits, and are the cause of the congealing in jellies.

In nature pectins and cellulose are broken down either by the enzyme cytase, which is not an ingredient of any known digestive juice, but is secreted by the cells themselves, and by various organisms, or by decomposition in the open air through the action of certain bacteria and moulds, or still further by fermentation under anaerobic conditions through the action of specific bacteria. It is this last-mentioned method which is of interest to us, because by just such a process cellulose can be broken down in the alimentary canal into carbon dioxide, methane, and such fatty acids as acetic, butyric, and valeric. It is known that cellulose does undergo some transformation in the bowels, because it is impossible to recover from the faeces the whole amount introduced in the food. Tappeiner has been able outside the body to dissolve as much as 70 per cent. of cellulose by means of the intestinal juices of the horse, which are rich in bacteria.

It is reasonable to suppose that something of the same kind takes place in the body, or that the cellulose is acted upon by the epithelium of the intestinal canal. The human intestine can dissolve a part of the tender cellulose of young vegetables, as much as 40 per cent. of the cellulose contained in them being unrecoverable in the faeces. It is quite possible that the valuable mechanical irritation produced by cellulose on the intestine is to a large extent lost when foods which contain it are cooked, and that in the uncooked system which we are considering the more efficient evacuation of the bowels which is likely to be present frees the body of toxins which would otherwise be absorbed.

But it must not be forgotten that these are just the circumstances in which excessive fermentation of carbohydrates is liable to take place, and this, of course, constitutes an important source of loss of potential energy in the diet through the conversion of the sugar or starch into carbon dioxide and the various acids mentioned above. Major McCay describes the effects of such a process in Bengali prisoners and others who, because of excessive intestinal fermentation, suffer from flatulency, tendency to diarrhoea and colic, and are accustomed to excrete faecal matter soft from admixture with gas, and light brown to yellow in colour for the same reason.

Schmidt has ascertained by personal observation that sufferers from chronic constipation are quite capable of utilising both raw and cooked vegetables; and even mushrooms, which are the most resistant of all cellulose-containing plants, are completely disposed of. This is due to some agency at present unknown, because when constipation is induced in a normal healthy subject his coefficient of assimilation is not increased. There are, however, perfectly normal individuals who are able to assimilate raw vegetables, and these are true vegetarians or herbivora, whereas those who are unable to utilise them he designates carnivora. He has demonstrated that the more marked the gastric acidity the more vegetable matter is digested, and this is due to the solution of the cement between the cell walls, which is composed of pectins and hemi-cellulose. This process is strictly comparable to the digestion in the stomach of the connective tissue between the fibres of meat.

Nor must we lose sight of the fact that raw starch is by no means easily digested. Whether it be administered in potatoes or cereals, only a very small portion of raw starch is capable of assimilation. It is therefore passed in the stools and has a very deleterious effect on the digestive processes. In starch manufactories certain of the employees become addicted to the habit of eating the starch, and rarely survive longer than a year. Profound disturbance of the organs of digestion and assimilation ensues, malnutrition supervenes, and intense anaemia - which is the objective of the unfortunate victim in her desire to obtain a more interesting if not more attractive complexion - becomes established before the fatal denouement.

Where the organs of digestion are already impaired the use of uncooked foods is by no means free from danger, and even when the digestion is good it is wise to give special attention to their careful mastication. I have seen more than once a most severe attack of acute dyspepsia arise in a subject of diminished gastric motility from eating a raw apple or other form of raw fruit. In any form of atonic dyspepsia all uncooked foods should be reduced to a liquid or pasty state in the mouth before swallowing, and any insoluble fibrous or other solid particles should be rejected.

Fruits in the ordinary acceptation of the term may be divided into two classes: (1) food fruits, some of which, like the fig, contain a fair percentage of protein; (2) acidulous watery fruits, containing from 75 to 95 per cent. of water, practically no protein or fat, from 25 per cent. of sugar in some grapes to 1 per cent. in lemons, and pectins which exert a demulcent effect on the bronchial mucous membrane. The valuable therapeutical influence of fresh fruit juices on the body is mainly due to citric, malic, and tartaric acids in combination with alkalis. These acids are converted into carbon dioxide in the organism, and the bicarbonate of potash thus formed is a potent alkalinising agency, all the more powerful because it is present in a nascent state. The alkali contained in a kilogram of strawberries is, according to Linossier, equivalent to 9 grams of sodium bicarbonate. The explanation of the valuable properties of raw fruit as compared with cooked fruit is that its mineral substances are combined with organic matters forming colloidal compounds. Most fruits have a diuretic action, partly due to the potash salts and partly specific, and in addition uncooked foods, both fruits and vegetables, possess the estimable quality of leaving a large indigestible residue in the bowel, which stimulates intestinal activity, hastens the movement of the intestinal contents, and so tends in a natural manner to lessen the inception of putrefactive processes. For short periods of time an inclusive diet of raw food may be adopted with benefit. The grape cure, the whey cure, the sour milk cure, the apple or exclusive fruit cure, are all occasionally of undoubted therapeutical value. Medical supervision for the patients undergoing these treatments is absolutely essential if beneficial results are to be obtained, and, needless to say, prolonged adherence to any of them is to be strictly avoided.