252 EXPERIMENTAL PHARMACOLOGY 



stand it and continue giving the drug until several centi- 

 meters are injected. Wait a while to observe the effect 

 on urine flow. This often fails in dogs. Why? Will the 

 chloral influence the result in any way! 



Wait for fifteen or twenty minutes for the caffeine to 

 act. Be sure the dose given was large enough. Then al- 

 low the animal to become as nearly normal as possible and 

 get a new normal rate of urine flow. Test the urine for 

 sugar. What do you observe! Explain. 



Now empty the caffeine out of the burette and fill it with 

 four per cent sodium sulphate solution. Inject one cubic 

 centimeter. Increase the dose rapidly (twenty cubic cen- 

 timeters or more may be given at a time often without 

 killing the animal) and watch the effect on blood-pres- 

 sure, respiration and urine flow. What do you observe I 

 How does this compare with the action of caffeine! If 

 the animal is still in fair condition substitute a four per 

 cent solution of sodium phosphate (or nitrate or chloride) 

 for the sodium sulphate and inject a considerable quantity 

 of this salt. How is the rate of urine flow affected! What 

 theories of urine secretion do you know! On the basis of 

 these explain the action of the drugs injected. Keep a 

 record of the amount of solution injected in each ten min- 

 ute interval and see if you can collect an equal volume of 

 urine in a beaker in the same time. This can sometimes 

 be done, especially with rabbits. Kill the animal by a 

 large injection of one of the salts mentioned (watching the 

 urine flow as the drug is acting), then dissect out the pan- 

 creas and see if you can find its lower duct (Figs. 244 and 

 L'45). Could you put a cannula in the duct while the ani- 

 mal was alive ? Dissect out the gall bladder, the cystic 

 duct, and the common duct. What are the relations of the 

 pancreatic ducts and the bile ducts as they pass through the 

 wall of the intestine .' 



