FOOD AND DIGESTION. 383 



working of the body, in some unknown way, just as the products of the 

 thyroid gland are. 



The formation of the decomposition products indol and skatol is 

 caused by the action of bacteria on proteids, and will bespoken of under 

 another heading. 



The albuminous or proteid substances which have not been converted 

 into peptone and absorbed in the stomach, and the partially changed 

 substances, i.e., the proteoses, are converted into peptone by the pan- 

 creatic juice, and then in part into lencin and tyrosin. 



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

 also in a neutral medium, or in the presence of a small amount of com- 

 bined 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, proteid mat- 

 ter does not swell up at first but seems to be corroded. 



(2.) Starch is converted into maltose in an exactly similar manner to 

 that which happens with saliva, erythro-dextrine and one or more achroo- 

 dextrines being the intermediate products. The arnylolytic enzyme of 

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

 called amylopsin. The maltose thus formed is converted to dextrose 

 either just before or during its absorption, in which form it passes into 

 the blood. This conversion is in part due to the action of the enzyme 

 glucase. 



(3.) Pancreatic juice possesses the property of curdling milk, contain- 

 ing 1 a special (rennet) ferment for that purpose. The ferment is distinct 

 from trypsin, and will act in the presence of an acid (W. Roberts). It is 

 best extracted by brine. The milk-curdling ferment of the pancreas is, 

 in some pancreatic extracts, extremely powerful, insomuch that 1 cc. of 

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



(4.) Oils and fats are emulsified and saponified by pancreatic secre- 

 tion. The terms emulsijication and saponification may need a little ex- 

 planation. The former 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 particles. If a email 

 drop cf an emulsion be looked at under the microscope it will be seen 

 to be made up of an immense number of minute rounded particles of 

 oil cr fat, of varying sizes. The more complete the emulsion the smaller 

 are these particles. An emulsion is formed at once if oil or fat, 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 a fat being made 

 up chemically of glycerin, a triatomic alcohol, and one or more fatty 

 acid radicles, when an alkali is added to it, and heat is applied, two 



