340 SECRETION OF GASTRIC JUICE. [Boos n. 



orifice. When food was introduced into the main stomach secretion 

 also took place in the isolated fundus. This at first sight might 

 seem the result of a nervous reflex act ; but it was observed that 

 the secondary secretion in the fundus was dependent on actual 

 digestion taking place in the main stomach. If the material 

 introduced into the main stomach were indigestible or digested 

 with difficulty, so that little or no products of digestion were 

 formed and absorbed into the blood, such ex. gr. as pieces of 

 ligamentum nuchse, very little secretion took place in the isolated 

 fundus. We quote this now as bearing on the question of a 

 possible nervous mechanism of gastric secretion, but we shall have 

 to return to it under another aspect. 



The changes in a gland constituting the act of secretion. 



195. We have now to consider what are the changes in the 

 glandular cells and their surroundings which cause this flow of 

 fluid possessing specific characters into the lumen of an alveolus, 

 and so into a duct. It will be convenient to begin with the 

 pancreas. 



The thin extended pancreas of a rabbit may, by means of 

 special precautions, be spread out on the stage of a microscope 

 and examined with even high powers, while the animal is not only 

 alive but under such conditions that the gland remains in a nearly 

 normal state, capable of secreting vigorously. It is possible under 

 these circumstances to observe even minutely the appearances 

 presented by the gland when at rest and loaded, and to watch 

 the changes which take place during secretion. 



When the animal has not been digesting for some little time, 

 the outlines of the individual cells lining the alveolus are very in- 

 distinct, the lumen is invisible or very inconspicuous, and each 

 cell is crowded with small, refractive spherical granules, forming 

 an irregular granular mass which hides the nucleus and leaves 

 only a very narrow clear outer zone next to the basement mem- 

 brane, or it may be hardly any such zone at all. Fig 77 A. The 

 gland is said to be ' loaded ' or at rest. 



The blood-supply moreover is scanty, the small arteries being 

 constricted and the capillaries imperfectly filled with corpuscles. 



If, however, the same pancreas be examined while it is in a 

 state of activity, either from the presence of food in the stomach, 

 or from the injection of some stimulating drug, such as pilocarpin, 

 a very different state of things is seen. The individual cells 

 (Fig. 77 B) have become smaller and much more distinct in 

 outline, and the contour of the alveolus which previously was even 

 is now wavy, the basement membrane being indented at the 

 junctions of the cells ; also the lumen of the alveolus is now wider 

 and more conspicuous. In each cell the granules have become 



