30 



THE GASTRIC JUICE 



" These two opposed views, resulting rather from 

 observations than from regularly instituted experi- 

 ments, were the starting-point of the experimental 

 researches undertaken by Reaumur in 1752. To 

 resolve the problem set by Borelli and Valisnieri, 

 Reaumur made birds swallow food enclosed in 

 fenestrated tubes, so that the food, protected from 

 the mechanical action of the walls of the stomach, 

 was yet exposed to the action of the gastric fluid. 

 The first tubes used (glass, tin, etc.) were crushed, 

 bent, or flattened by the action of the walls of the 

 gizzard ; and Reaumur failed to oppose to this 

 force a sufficient resistance, till he employed leaden 

 tubes thick enough not to be flattened by a 

 pressure of 484 pounds : which was, in fact, the 

 force exercised by the contractile walls of the 

 gizzard in turkeys, ducks, and fowls under obser- 

 vation. These leaden tubes — filled with ordinary 

 grain, and closed only by a netting that let pass 

 the gastric juices — these tubes, after a long stay 

 in the stomach, still enclosed grain wholly intact, 

 unless it had been crushed before the experiment. 

 When they were filled with meat, it was found 

 changed, but not digested. Reaumur was thus 

 led at first to consider digestion, in the gallinacese, 

 as pure and simple trituration. But, repeating these 

 experiments on birds of prey, he observed that 

 digestion in them consists essentially in dissolution, 

 without any especial mechanical action, and that 

 it is the same with the digestion of meat in all 

 animals with membranous stomachs. To procure 

 this dissolving fluid, Reaumur made the birds 

 swallow sponges with threads attached : with- 

 drawing these sponges after a definite period, he 

 squeezed the fluid into a glass, and tested its 

 action on meat. That was the first attempt at 



