322 Dr. R. D. Thomson on the 



viency to the solvent powers of the animal system would be 

 removed. This view of the case is fully borne out by a refer- 

 ence to the form in which the flour of the various species of 

 Cerealia is employed as an article of food by different nations. 

 By the peasantry of Scotland, barley-bread, oat-cakes, peas- 

 bread, or a mixture of peas- and barley-bread, and also po- 

 tatoe-bread mixed with flour, are all very generally employed 

 in an unfermented form, with an effect the reverse of injurious 

 to health. With such an experience under our daily obser- 

 vation it is almost superfluous to remark, that the Jew does 

 not labour under indigestion when he has substituted, during 

 his passover, unleavened cakes for his usual fermented bread, 

 — that biscuits are even employed when fermented bread is 

 not considered sufficiently digestible for the sick, and that the 

 inhabitants of the northern parts of India and of Affghanistan 

 very generally use unfermented cakes, similar to the scones of 

 Scotland. 



Such then being sufficient evidence in favour of the whole- 

 someness of unfermented bread, it becomes important to dis- 

 cover in what respect it differs from fermented bread. Bread- 

 making being a chemical process, it is from chemistry alone 

 that we can expect a solution of this question. In the pro- 

 duction of fermented bread, a certain quantity of flour, water 

 and yeast are mixed together and formed into a dough or 

 paste, which is allowed to ferment for a certain time at the ex- 

 pense of the sugar of the flour. The mass is then exposed in 

 an oven to an elevated temperature, which puts a period to 

 the fermentation, expands the carbonic acid resulting from the 

 decomposed sugar and the air contained in the bread, and 

 expels the alcohol formed and all the water capable of being 

 removed by the heat employed. The result gained by this 

 process the author considers to be merely the expansion of 

 the particles of which the loaf is composed, so as to render the 

 mass more readily divisible by the preparatory digestive or- 

 gans. But as this object is gained at a sacrifice of the inte- 

 grity of the flour, it becomes a matter of interest to ascertain 

 the amount of loss sustained in the process. To determine 

 this point the author had comparative experiments made upon 

 a large scale with fermented and unfermented bread. The 

 latter was raised by means of carbonic acid generated by 

 chemical means in the dough ; but to understand the circum- 

 stances some preliminary explanation is necessary. 



Mr. Henry of Manchester, at the end of the last century, 

 suggested the idea of mixing dough with carbonate of soda and 

 muriatic acid, so as to disengage carbonic acid in imitation of 

 the usual effect of fermentation ; but with this advantage, that 



