MESSRS. EDITORS—Dr. Montague appears to be greatly alarmed lest the use of soda water, so called, and unfermented bread should injure the health of the community. His statements of the physiological and chemical nature and changes of the substances referred to, are so vague and mistaken that I am not surprised he should entertain this opinion. He speaks of the effervescing drink sold as soda water as containing soda, whereas there is not a particle of soda used in the manufacture of it; the effervescence being produced by the escape of carbonic acid gas, which has been forced into pure water, the gas itself being obtained from carbonate of lime by means of sulphuric acid. I suppose the doctor's patients, whose stomachs were in a state of morbid sensibility, must have imbibed something stronger than soda water. He also thinks that bi-carb. soda, tart, acid, cream tartar, c, used to raise bread, cake, c, must produce the same lamentable-consequences on the system, and he further accuses these substances ot producing acetous fermentation, when mixed with flour. Here again he is very unfortunate in his statement of facts, lor, after a very large experience on this point, I have never known this prepared flour to turn sour even in the most trying summer weather. He is equally at fault in his philosophy fif the process of fermentation ; this he describes as the union of moisture with the gluten ot the flour; now the acid in flour is not formed from any of the particles composing the gluten, but from the sugar and starch, the gluten being transformed into an entirely different substance. Our knowledge of the changes which our food undergoes in the system is not extensive, but we do know the changes which take place in the substances alluded to; when bi-carb-soda and tart, acid are mixed with flour, on the addition of water and heat the bi-carb. soda is decomposed, the carbonic acid escaping in the form of gas, raises the dough, the soda, uniting with the tart, acid, forms tar-trate ot soda; this is taken into the stomach with the bread, and in passing through the system, is again decomposed ; its tartaric acid disappears, and by the addition of oxygen is converted into carbonic and water, the soda passing out ot the system in the urine as a carbonate. Thus it is evident there is no alkali to injure the gastric juice or stimulate the stomach to morbid sensibility, consequently the doctor's fears are utterly unfounded. It can scarcely be necessary to say that the class of acids to which cream tartar belongs, do not produce the injuries which the doctor specifies, for the experience of mankind is unusual that grapes, apples, c, which contain large quantities of these acids, are wholesome fruit, Newark, N. J. C. DOWDEN. [Dr. Montague's letter appeared on page 267 ; he made no personal allusions, and employed no offensive language; if he entertains wrong opinions, our present correspondent's letter does not exhibit the proper spirit which should characterize a man anxious to do good, by correcting errors in others. In respect to the so-called " soda water," sold as a summer beverage, our present correspondent is right regarding its composition, but Dr. Montague is right respecting its effect. " Its frequent repetition as a beverage," in a case within the compass of our own observation, completely destroyedthe health, by injuring the stomach of a once healthy man; but Dr. M. stated that soda water, as an effervescing mixture, it taken in moderate quantities, might be useful in correcting acidity of the stomach. Dr. M. did not say that true fermentation was produced by the union of moisture and an alkali with the gluten of flour. The sugar, which is never absent from true fermentation, is a product from the starch itself; it is not found in pure flour. In the manufacture of starch, a small quantity of lactic acid is produced in the steeping of the grain; this unites with the gluten and sets the starch free j alkalies are employed to produce th" same effect. The vegetable fibrine in the gluten o flour is rendered soluble by alkaline liquors, and is very prone to decompose but we do not see how it is possible that such small quantities of acid, bi- carbonate of soda, and sugar, as are used in flour for quick fermentation, can be injurious to the stomach. At the same time Dr. Montague, may, in his experience, have reasons for thinking otherwise. Carbon, we know, forms a prominent part of the food ot man, but it would not do to feed upon it. A correct knowledge of the best foods and drinks, beneficial and injurious to man, can only be obtained by experience. Wines are not reckoned healthy until they have deposited their bi-tartrate of soda, on the sides of the vessels in which they are contained. What is called " unfermented wine," is not wine at all.