TEX RABBIT. 17 



under ordinary circumstances, are closed, but which relax 

 to open the circular central aperture. The valve at the 

 anus, which retains the faeces, is another instance of a 

 sphincter. When, by the relaxation of the pylorus, some of 

 the chyme is allowed to enter the duodenum, it is met by 

 the green bile, secreted by the Ever, stored up in the gq.ll- 

 bladder, and poured into the duodenum along the bile-dnp.f.. 

 The bile seems to have more than one function, and the 

 exact help which it gives to digestion is somewhat uncertain. 

 It is alkaline, and thereby neutralizes the acidity of the 

 chyme and puts an encl toj^ft .pfa'nn 



extent it also emulsifies the fats (i.e. breaks them up into 

 minute oily globules), in both these ways it may help to 

 prepare the chyme for the next fluid it meets 



creatic juice. There is no doubt, however, that a good part 

 of the bile is merely waste material, destined to pass out 

 with the faeces. In so far as this is the case, the bile may 

 be put down among the excretions, though, unlike urine and 

 sweat, it is an excretion of which some use is made. As we 

 shall see in the next chapter, the secretion of bile is by no 

 means the sole function of the liver. It seems also that 

 the bile has an antiseptic action, i.e. that it checks the 

 development of bacteria in the chyme. Its aotion in this 

 way, however, is not very great, as bacteria (a few having 

 escaped destruction by the gastric juice) multiply and 

 abound throughout the intestines. 



12. The Pancreatic Juice. Little more than half-way 

 along the duodenum the chyme is met by the pancreatic 

 juice, secreted in the pancreas. This fluid is alkaline 

 (through the presence of sodium carbonate) and has a 

 complicated action on the chyme, as it contains several 

 ferments. One called amylopsin acts (like ptyalin) on 

 starch, converting__it_in.to "g"ar; another T trypsin, carries 

 on" the work of pepsin^ from which it differs by acting only 

 in alkaline, not acid, fluids. The alkalinity of the pancreatic 

 juice also leads to the more complete emulsification of the_ 

 ffiffi a.nd nils, and these, when thoroughly divided np into 

 drpplfit-a, arfr antpd on_by a thirjLieynicnt, otoapsin, and 

 each is split up (chemically) into gl^cerme^md one of the 

 ZOOL. 2 



