78 PHYSIOLOGY FOR DENTAL STUDENTS. 



(antipepsin, antitrypsin, etc.). As we should expect, very strong 

 anti-enzymes can be prepared from tapeworms and other intes- 

 tinal worms. It is in virtue of possessing these, that the worms 

 are not digested. The immunity of the gland cells and ducts, as 

 of the pancreas, to the proteolytic enzymes which they produce 

 is possibly to be explained in another way, namely, by the ex- 

 istence of the enzyme as an inactive precursor (e. g., trypsino- 

 gen) until after the secretion has been carried to a region whose 

 walls contain the specific anti-body. A certain degree of im- 

 munity to a possible destructive action of the intestinal bacteria 

 may be conferred by the mucin, which is quite abundant, at least 

 in the empty stomach and in the large intestine. The relatively 

 poor growth of bacteria which occurs on inoculating faecial mat- 

 ter in culture media although many bacteria can be seen by 

 microscopic examination to be present is probably to be ex- 

 plained by their having been killed by the mucin. 



The Movements of the Intestines. 



The movements of the small intestine have two functions: (1) 

 to macerate and mix up the food and "('2) to move it along to- 

 wards the lower end of the gut. These two functions are sub- 

 served by two different types of movement, the so-called pendular 

 and the peristaltic. The pendular movements are rendered evi- 

 dent by allowing the intestine to float out in a bath of isotonic 

 saline, when the various loops sway from side to side like a pen- 

 dulum. By closer examination it can be seen that the movements 

 are produced by faint waves of contraction of both muscular 

 coats which sweep with considerable rapidity along the gut. 

 When the waves arrive at a part of the intestine containing any 

 solid substance, they become accentuated, and this becomes most 

 marked at the middle of the solid mass of food, thus tending, on 

 account of the contraction of the circular fibers, to divide the 

 mass into two. They are therefore sometimes called segmenting 

 movements. Beyond the mass the contractions again fade away. 

 Their function is evidently to break up the food masses and thus 

 mix them with the digestive juices. This can be very well shown 

 in skiagram shadows of the abdomen some time after taking food 



