88 PERMEABILITY AND ACTIVE TRANSPORT 



Exercise XVII 



inside out), filled with the solution to be studied, 

 and tied off at both ends to form sausage-like 

 sacs. The eversion places the serosal side toward 

 the inside of the sac, and the mucosal side out- 

 ward, so that the cells engaged in active transport 

 can be kept supplied with oxygen. The sac is laid 

 in the same solution it contains, and incubated 

 with continuous aeration for some time. After 

 incubation, the solutions inside and outside the 

 sac are analyzed to reveal any change of concen- 

 tration that may have occurred. 



The hamster gut should be set up as described 

 below as soon as you enter the laboratory. 

 There are, however, several things that should 

 be done during the 60 to 90 minutes of incuba- 

 tion. During this time the materials for the 

 glucose analysis should be prepared. It would be 

 wise to run through the analysis of the standard 

 solution to make sure that everything is working 

 well. 



The hamster from which you removed the gut 

 should also be used to review vertebrate anat- 

 omy. Trace the alimentary canal. Examine the 

 prepared slides of intestinal tissues. Review also 

 the circulatory system. Compare the hamster 

 heart with that of the frog. Note the cheek 

 pouches. What do you notice about the hamster 

 stomach ? 



Try to find the major places in the body where 

 substances pass from one "compartment" to the 

 other. In which of these is one "compartment" 

 the outside environment, or open to it? In this 

 connection, do you regard the inner cavity of the 

 gastrointestinal system as inside or outside the 

 animal? How about the body cavity (coelom)? 

 Does it possess an opening to the outside en- 

 vironment, not blocked by a membrane? in 

 males? in females? 



One of the principal organs for the exchange of 

 dissolved substances is the kidney. Portions of 

 the kidney provide prime examples both of diffu- 

 sion through a semipermeable membrane, and 

 active transport (cf. Homer Smith's article listed 

 in the Readings). Examine the hamster kidney. 

 Examine also the prepared slides, and identify 

 Bowman's capsule, glomerulus, and tubules. 

 Which substances are excreted by the kidney? 



Which retained? Where do these things occur, 

 and what kinds of permeability are involved? 



PROCEDURE 



Students, working in pairs, will be given a 

 freshly killed hamster. Slit open the belly so as 

 to expose the viscera, being careful not to dam- 

 age the intestine. Find the stomach. Snip off 

 the upper end of the duodenum just below the 

 stomach, and carefully uncoil the small in- 

 testine, using scissors to cut away the mesentary 

 when necessary. When the lower end of the small 

 intestine is reached, snip it loose, and place the 

 entire intestine in a petri dish half filled with 

 Krebs phosphate Ringer solution containing 20 

 millimolar (0.36%) glucose. Do not allow the 

 intestine to dry! 



All the remaining mesentery and fat should be 

 stripped by hand from the gut. Cut the intestine 

 into at least two (preferably three or four if 

 your animal is large) 5- or 6-cm sections, begin- 

 ning at the upper end. Using a dropper, gently 

 force a little solution through the sections to 

 wash out the contents. 



The sections of gut are now ready to be 

 everted and tied off. 



The mucosal surface is extremely delicate and 

 the success of your experiment depends upon it. 

 Handle it as little and as gently as possible, 

 taking special pains not to scrape or bruise it. 

 Using the glass rods provided, push one end of 

 the gut into the lumen until it appears at the 

 opposite end. Complete the eversion by rolling 

 the gut along the rod. Slip the gut off the rod, 

 and immerse in fresh glucose-Ringer solution. 



Tie a thread ligature tightly around one end. 

 Fill a dropper with the glucose-Ringer solution 

 and insert the dropper into the gut. Loosely 

 knot a thread around the open end of the gut so 

 that it can be tightened quickly. Force the solu- 

 tion from the dropper into the intestinal sac until 

 the sac is completely filled but not grossly dis- 

 tended. Tighten the ligature quickly as the 

 dropper is withdrawn. 



Place the sac in a test tube containing 5.0 ml of 

 the fresh glucose-Ringer solution, and leave it at 



