Scientific Lectures. 119 



cooled bread in hermetically sealed spaces and it became stale. He 

 then sealed stale bread in a metallic tube and heated it. It became 

 fresh, and again stale on cooling. He repeated the process, in all 

 forty times, with the same sample, alternately heating and cooling, 

 and with the last heating it became fresh, and with the last cooling it 

 l)ecame stale. He concluded from his experiments that there was 

 what he called a molecular change taking place in the crumb when it 

 became stale, and again when it became fresh, and he thought he had 

 explained it. Thenard, who listened to Boussingault's paper before 

 the Academy, suggested that bread was a hydrate, from which water 

 was driven out by heat, and reabsorbed on cooling. But it would 

 Beem, according to this view, that fresh bread, to the taste, should be 

 the di-yer of the two. Neither explanation was satisfactory. When 

 I found that gluten was a hydrate, from which a moderate heat would 

 expel water, and that, on cooling, this water was again taken into the 

 constitution of the gluten, I applied this fact to the solution of the pro- 

 blem. The stale crumb may be regarded as a framework of gluten 

 coated with glassy dried starch, which is not readily dissolved by 

 saliva. Of course, when taken into the mouth, it requires time before 

 it becomes flexible, and can be easily compressed to force out the 

 fluids it takes up in the mouth by virtue of its capillary action. But 

 by heating, the water of hydration of the gluten is driven out, the 

 starch which invests the gluten is moistened and rendered flexible, 

 and the whole crumb, recovering the sponge-like elasticity of fresh 

 bread, yields its juices when masticated, and is palatable. To test 

 this, I placed in a glass tube a quantity of gluten, and sealed it up. I 

 then placed the end containing the gluten in warm water, andbelield, 

 a few moments later, moisture conder.!-e on the interior of the upper 

 end of the tube, which was cool. On withdrawing the tube from the 

 water, after a few hours, the film of moisture had disajjpeared. 

 Water had been driven out from the gluten by heat, and had been 

 real)sorbed on cooling. I then placed another quantity of gluten in 

 the bottom of a tube, above it a tuft of cotton, and above the cotton 

 a quantity of loose shavings of very thin glacial starch. ISTow I 

 expected that if moisture was given oft' from the gluten, it would 

 penetrate to the space occupied by the shavings, half liquify the 

 starch, and make it adhesive. In this condition the starch shavings 

 would be gummed fast to the glass, and it would no longer be possible 

 to shake them about. The experiment realized my expectations. 

 The solution, then, of the question of the difterence between stale and 



