DIGESTIBILITY OF BREADS. 73 



Now, though one can scarcely c-ouceive of any other than a clogging action on the 

 part of insoluble salts, yet in the above experiments, the hydrate and phosphate of 

 aluminium seem to induce a condition more unfavourable to ferment action than would 

 be the case if their influence were purely mechanical. It has been suggested that neutral 

 salts may form compounds with the ferment, which have of themselves little or no 

 digestive power. This offers an explanation for the marked retarding powers of soluble 

 sulphates, which, however, can scarcely be made to apply to insoluble pulpy precipitates. 

 Eccles, in the paper referred to above, found that sulphates as a rule possess a greater 

 retarding influence on peptic digestion than other class of salts. This is fully in accord 

 with my experiments on the amylolytic ferment of saliva. That the acid sodium phos- 

 phate shews the highest retarding action is at first sight anomalous, but this must be due 

 entirely to its acidity, and not to any inherent property of the acid or base of the salt, 

 because the same quantity of the neutral phosphate seems quite innoxious. 



Conclusions. 



In comparing the results described under Divisions A and B with those of Division 

 C, one seems quite justified in arriving at these conclusions. In the first place, the bread 

 made with the tartaric acid powder is most quickly digested, because the Rochelle salts 

 formed by the decomposition of this baking mixture possess a very weak retarding 

 influence on ferments. On the other hand, the presence of alkaline sulphates and of the 

 pulpy viscid hydrate and phosphate of aluminium among the decomposition products of 

 the other powders, is quite sufficient to explain the relative indigestibility of bread con- 

 taining these salts. That every experiment should have shewn the alum powder to be 

 the most noxious to the ferments, is manifestly due to the combined retarding influence 

 of two agents left in the bread by this mixture, viz., an alkaline sulphate and the phos- 

 phate of aluminium. 



The phosphate powder, it must be remembered, contained about 13 % of a sulphate 

 (CaSOj) which probably accounts for its high retarding power. Soluble phosphates 

 do not appear to interfere seriously with the proper action of digestive ferments ; at all 

 events no experimenter has found them possessed of that specific retarding power which 

 is so characteristic of the sulphates as a class. 



Generally then the inferences to be drawn from these experiments do not coincide with 



with the views usually expressed by either th(! opponents or the defenders of alum baking 



powders, though they may favour the former. Here, as is so often the case in hotly 



contested questions, the truth seems to lie between the extremes of opinion expressed by the 



two parties. For, on the one hand, there is nothing in common between the specific 



destructive action of alum itself and the semi-mechanical, retarding influence of these 



products of its decomposition. A quantity of alum that would entirely prohibit ferment 



action will (as shewn in Division C), when converted into its equivalent alkaline sulphate 



and aluminium phosphate, only delay digestion from 20 to 30%. On the other hand, 



although there is no similarity between the effects of alum itself and of the salts left in 



bread by akim baking powders, yet the retarding influ.ence of the latter on digestion is 



certainly well marked. 



Sec. iii, 1887. 10. 



