542 SPECIAL PHYSIOLOGY. 



and its quantity increases as digestion goes on, the activity of the 

 process being, by some, referred to the absorption of albuminoid sub- 

 stances already digested. From these fluctuations, it is impossible to 

 estimate correctly the quantity formed daily ; which has been differ- 

 ently estimated at from 7 oz. to 16J Ibs. Statements, almost as 

 discrepant, have been made concerning the gastric juice and bile, cor- 

 rect results, as regards these internal secretions, not being so attain- 

 able as in the case of the saliva. The collection of these fluids, by 

 aid of artificial fistulae, in animals, is open to the objection, that the 

 conditions, especially of the nerves, which govern the quantity of the 

 secretion, are not healthy. The total quantity of the digestive fluids 

 poured into the alimentary canal, after taking food, is, however, much 

 greater than was formerly supposed, and, in comparison with the 

 blood circulating in the body, is very great. 



The solid constituents of the pancreatic juice, as estimated from 

 cases of artificial fistulae in animals, vary from 1.5 to 6, or even 10 per 

 cent. ; the more rapid the secretion, the less solid matter it contains. 

 Its most peculiar constituent is an albuminoid substance named pan- 

 creatin, the special composition of which is not yet determined. Like 

 salivin, this substance is soluble in water, coagulable by heat, and pre- 

 cipitable by alcohol, but may again be dissolved in water ; unlike albu- 

 men, it is precipitated by sulphate of magnesia. To the pancreatin 

 are attributed the peculiar digestive properties of the pancreatic juice, 

 which differ, in one respect, most remarkably, from those of the saliva. 



The pancreas, indeed, resembles the salivary glands anatomically, 

 but not physiologically ; for its secretion is much more viscid, is coagu- 

 lated by strong mineral acids, and does not contain sulphocyanide of 

 potassium. Its salts, about .5 to 1.. per cent., are chiefly chloride of 

 sodium and phosphate of lime and magnesia. Like the saliva, it is 

 alkaline, but more strongly so ; as digestion proceeds, it becomes more 

 alkaline, but less viscid and coagulable. On standing, it speedily 

 becomes neutral and then acid ; it soon putrefies, but may be preserved 

 for a few days, at a temperature of 45 ; its properties are destroyed 

 by a heat slightly above that of the body. It contains the debris of 

 a few nucleated cells. 



Sources and Composition of the Intestinal Juices. 



The mucous membrane of the small intestine is provided with two 

 kinds of secreting glands, named respectively, after their discoverers, 

 the glands of Brunner and the glands, follicles, or crypts of Lieber- 

 kuhn. The secreted products of all these glands, constitute the 

 succus entericus. 



Brunner s glands are found in the duodenum, being most abundant 

 near the pylorus, and disappearing lower down, very few being present 

 at the commencement of the jejunum. They are compound racemose 

 glands, like the buccal and labial glands, and appear to bear the same 

 relation to the pancreas as those glands do to the salivary glands. 

 They secrete a viscid alkaline mucus. 



The follicles or crypts of Lieberkuhn are found throughout the small 



