THE SALIVARY GLANDS. 765 



He finds that the central cells in the fasting stage are charged with 

 granules, and that during digestion the granules are dissolved, dis- 

 appearing first from the base of the cell, which then becomes filled 

 with a non-granular material. Observations similar to those made 

 upon other glands demonstrate that these granules represent in all 

 probability a preliminary material from which the gastric enzymes 

 are made diu-ing the act of secretion. The granules, therefore, are 

 sometimes described as zymogen granules. 



Meanb of Obtaining the Gastric Secretion and its Normal 

 Composition. — The secretion of the gastric membrane is formed in 

 the minute tubular glands scattered over its surface. As there is no 

 common duct, the difficulty of obtaining the secretion for analysis 

 or experiment is considerable. This difficulty has been overcome 

 at different times by the invention of special methods. 



The older methods used for obtaining normal gastric juice were 

 very unsatisfactory. An animal was made to swallow a clean 

 sponge to which a string was attached so that the sponge could 

 afterward be removed and its contents be squeezed out; or it was 

 made to eat some indigestible material, to start the secretion of 

 juice; the animal was then killed at the proper time and the con- 

 tents of its stomach were collected. 



The experiments of the older observers on gastric digestion, especially 

 those of the Abbe Spallanzani (1729-1799), furnish most interesting reading. 

 Spallanzani, not content with making experiments on nmnerous animals 

 (frogs, birds, mammals, etc.) had the courage to carry out a great many 

 upon hiinself. He swallowed foods of various kinds and in various conditions 

 sewed in linen bags or mclosed in perforated wooden tubes which m turn 

 were covered with linen. The bags and tubes were subsequently passed 

 in the stools and were examined as to the amount and nature of their contents. 

 He seems to have experienced no injury from his experiments, although 

 normally his powers of digestion were quite feeble. As proof that the trit- 

 urating power of the stomach is not very great he caUs attention to the fact 

 that some of the wooden tubes were made very thin, so that the slightest 

 pressure would crush them, and yet they were voided uninjured. So also 

 he found that cherries and grapes when swallowed whole, even if entirely 

 ripe, were usually passed unbroken. 



A better method of obtaining normal juice was suggested by the 

 famous observations of Beaumont* upon Alexis St. Martin. St. 

 Martin, by the premature discharge of his gun, was wounded in the 

 abdomen and stomach. On healing, a fistulous opening remained in 

 the abdominal wall, leading into the stomach, so that the contents 

 of the latter could be inspected. Beaumont made numerous inter- 

 esting and most valuable observations upon his patient. Since that 

 time it has become customary to make fistulous openings into the 

 stomachs of dogs whenever it is necessary to have the normal juice 

 for examination. A similar surgical procedure is followed in human 



* Beaumont, "The Physiology of Digestion," 1833; second edition, 1847. 

 For a biographical account of Beaumont, see Osier, "Journal of the Ameriean 

 Medical Association," November 15, 1902. 



