PEPTIC DIGESTION 



59 



heating, and reappearing when the liquid cools. This last is a 

 distinctive property of proteoses. They are slightly ditfusible. 



The following table will give us at a glance the chief characters 

 of peptones and proteoses in contrast with those of native proteids 

 like albumin and globulin : — 



The difference between the different proteoses is mainly one of 

 solubility. The primary proteoses (proto- and hetero-) are precipitated 

 by saturation with magnesium sulphate or sodium chloride. Deutero- 

 proteose is not ; it is, however, precipitated by saturation with 

 ammonium sulphate. Proto- and deutero- proteoses are soluble in 

 water ; hetero-proteose is not ; it requires a salt to hold it in 

 solution. 



To sum up : the main action of the gastric juice is upon the pro- 

 teids of the food, converting them into more soluble and diffusible 

 products. The fats are not chemically altered in the stomach ; 

 their proteid envelopes are, however, dissolved, and the solid fats 

 are melted. Starch is unaffected ; but cane sugar is inverted. The 

 inversion of cane sugar is largely due to the hydi-ochloric acid of the 

 juice, and is frequently assisted by inverting ferments contained in 

 the vegetable food swallowed. 



' In the case of deutero-albumose this reaction only occnrs in the presence of 



excess of salt. 



