286 SCIENCE PROGRESS 



deductions as scientifically justified by the facts he has himself 

 established ; some explanation is required of the attitude he 

 has adopted in coming to such illogical conclusions. 



Physiological Effects 



Turning to the physiological effect of bleaching, the evidence 

 available is mainly that given by expert witnesses in the patent 

 trial referred to. Ladd and White, experimenting in North 

 Dakota, U.S.A., showed that rabbits were rapidly killed by 

 alcoholic extracts of bleached flour and inferred the presence 

 of a toxic substance, probably a diazo-compound. Subsequent 

 observers have failed to confirm these results and they are 

 generally discredited. Halliburton states that traces of nitrites 

 have an inhibiting effect on the action of digestive enzymes 

 and infers that bleached flour would act likewise ; his experi- 

 ments, however, are not of a character to carry any weight 

 with those who are conversant with the behaviour of enzymes 

 in presence of metallic salts such as the nitrites. 



On the other hand, numerous investigators have failed to 

 find the slightest toxic action associated with either properly 

 bleached flour or its extracts. Fortunately the Local Govern- 

 ment Board has settled this vexed question for all time by 

 securing the assistance of Dr. A. Harden, F.R.S., a worker 

 whose repute justifies entire confidence in his experiments. 

 An account of his observations is published as an appendix to 

 the report. 



Dr. Harden's conclusion is very straightforward — the extract 

 from commercially bleached flour, from overbleached flour and 

 even that from grossly overbleached flour is apparently harm- 

 less to animals. With regard to enzymic digestion, he finds 

 that the bleaching of flour does not in any way diminish the 

 readiness with which it undergoes tryptic digestion in glass 

 vessels. Peptic digestion seems to be slightly inhibited by 

 bleaching but the differences observed were very small and it 

 may be doubted whether they have any significance. 



Flour containing ninety parts of nitrite per million was 

 found by Dr. Monier-Williams to retard salivary digestion; 

 commercially bleached flour had no effect. Dr. Hamuli's final 

 corollary is that highly bleached flour cannot be regarded as 

 free from risk to the consumer and that even in the case of 

 flour bleached by the methods in vogue at present it would 



