382 FOOD AND DIGESTION 



Protein 

 Proteoses 

 Peptones 



Polypeptids Amino-acids 



Combinations of proline, phenyl- Tyrosine, tryptophane, cystine, 



alanine and glycocoll, with rela- alanine, amino-valerianic acid, 



tively small amounts of alanine, leucine, aspartic acid, glutam- 



leucine, asparaginic acid, and inic acid, histidine, lysine, argi- 



glutaminic acid. nine. 



The ferment trypsin acts best in an akaline medium, but will act also 

 in a neutral medium, or in the presence of a very small amount of combined 

 acid; it will not work in the presence of free acid. It therefore differs from 

 pepsin in being able to act without the aid of any other substance than water. 

 In the process of tryptic digestion, protein matter does not swell up at first,, 

 but seems to be corroded at once. 



Amylopsin. Starch is converted by amylopsin into maltose by hydro- 

 lytic action similar to that of ptyalin, ery thro- dextrin and one or more 

 achroo-dextrins being the intermediate products. The amylolytic enzyme 

 of the pancreatic juice, which cannot be distinguished from ptyalin, is called 

 amylopsin. The maltose thus formed is converted to dextrose by the maltase, 

 in which form it is ultimately absorbed. 



Pancreatic juice, according to certain observers, possesses the property 

 of curdling milk. It contains a special ferment, rennin, for that purpose. 

 The ferment is distinct from trypsin, and will act in the presence of an acid 

 (W. Roberts). The milk-curdling ferment of the pancreas is, in some pan- 

 creatic extracts, said to be quite powerful, insomuch that i cc. of a brine ex- 

 tract will coagulate 50 cc. of milk in a minute or two. 



Steapsin orLipase. Oils and fats are emulsified and saponified by the pan- 

 creatic secretion. The terms emulsification and saponification may need a 

 little explanation. The term emulsification is used to signify an important 

 mechanical change in oils or fats, whereby they are made into an emulsion 

 or, in other words, are minutely subdivided into small microscopic particles. 

 If a drop of an emulsion be looked at under the microscope, an immense 

 number of minute rounded particles of oil or fat of varying sizes will be 

 seen. The more complete the emulsion the smaller are these particles. In 

 milk, which is a splendid example of an emulsion, the fat droplets vary in 

 diameter between i and 5^. An emulsion is formed at once if oil, which 

 when old is slightly acid from the presence of free fatty acid, is mixed 

 with an alkaline solution. 



Saponification signifies a distinct chemical change in the composition 

 of oils and fats. An oil or fat being made up chemically of glycerin, a 



