CH. XXXII.] NERVES OF THE PANCREAS 493 



extract, as steapsin is not soluble in glycerin : either the fresh juice 

 or a watery extract of pancreas must be used. 



The formation of an emulsion may be studied in the following 

 way : if olive oil and water are shaken up together, and the mixture 

 is allowed to stand, the finely divided oil globules soon separate, run 

 together, and form a layer which floats on the surface of the water. 

 But if olive oil is shaken up with a solution of soap, the conditions of 

 surface tension are such that the oil globules remain as such in the 

 mixture, and a white milky fluid called an emulsion is the result. 

 The emulsion is still more permanent if a colloid material like gum or 

 albumin is also present. Pancreatic juice possesses all the necessary 

 qualifications for the formation of an emulsion ; it is alkaline, and so 

 liberates fatty acids from the fat ; these acids form soap with the alkali 

 present ; moreover, it is viscous from the presence of proteid. 



4. Milk-curdling Ferment. The addition of pancreatic extracts 

 or pancreatic juice to milk causes clotting ; but this action (which 

 differs in some particulars from the clotting caused by rennet) can 

 hardly ever be called into play, as the milk upon which the juice has 

 to act has been already curdled by the rennin of the stomach. 



Secretory Nerves of the Pancreas. 



It has been known since the work of Claude Bernard in 1856 

 that the introduction of ether into the stomach produces a reflex flow 

 of pancreatic juice, but all attempts to discover the path of the nerve 

 impulses failed until the recent work of Pawlow. The reason of the 

 failure of previous workers is that the pancreas is remarkably sensi- 

 tive to external conditions. If the pancreas is cooled or wounded 

 during the process of making the fistula, or if sensory nerves are 

 excited, or if anaesthesia is deep, the gland refuses to secrete. 



Pawlow discovered that the vagus contains the secretory nerves of 

 the pancreas ; he took care to avoid the sources of error just referred 

 to. In the first place, he stimulated the vagi below the origin of their 

 cardiac branches ; in the second, the spinal cord was divided high up 

 to prevent reflexes occurring from sensory nerves; and lastly, the 

 operation of stimulating the nerve was done without an anaesthetic. 



In another series of experiments, he cut through one vagus in the 

 neck, and stimulated the peripheral end two or three days later, when 

 the cardio-inhibitory fibres had degenerated : in this way he got rid 

 of the heart stoppage, which would have interfered with the normal 

 condition of the animal. 



The stimulation of the vagus usually produced an abundant flow 

 of pancreatic juice, after a latent period of from fifteen seconds to two 

 minutes. The stimulation applied to the nerve consisted of a slow 

 series of shocks (either induction currents or mechanical blows) about 

 once a second. By this means stimulation of vaso-constrictor nerves 



