24 



THE WORK OF THE DIGESTIVE GLANDS. 



the changes both quantitative and qualitative, which the food and its 

 admixed secretion undergo, are followed, step by .step, throughout the 

 whole alimentary canal. 



We now pass on to a further question. If the glands, as we have 

 seen, are in a position to vary their work so remarkably, with regard 

 to the quantity of juice which they produce, are they not also able to 

 extend similar variations to the properties of the secretion ? Judging 

 from a theoretical standpoint, one would expect that in different phases 



in 



IV 



in 



IV 



it. 



14 



10 



FK;. 4. Curve of secretion of pancreatic juice. 

 Food, 000 cc. milk. (Two experiments.) 



of the digestion of the same food, a juice of varying properties would be 

 necessary. The total mass of food can have so altered, both in chemi- 

 cal and physical respects, under the influence of the first portions of 

 juice, that it may need for its further digestion a juice of different com- 

 position. Thus, more or less water, or a varying degree of acidity or 

 alkalinity, or a different content of ferment in the fluid, may be re- 

 quired. All these separate conditions of juice activity are naturally not 

 without importance. But so long as we dealt only with digestive 

 experiments performed in vitro, we could render no account of these 

 matters. It is tiue that science has long since answered our question 



