76 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



virtue of its NH 2 groups, and also of an acid in virtue of its 

 COOH groups. 



2. Proteoses. These are the intermediate products in the 

 hydrolysis of native proteins into peptones. 



They are not coagulated by heat ; they are precipitated but not 

 coagulated by alcohol ; like peptone they give the biuret reaction. 

 They are precipitated by nitric acid, the precipitate being soluble on 

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

 distinctive property of proteoses. They are slightly diffusible. 



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. 



3. Peptones. These are the final products of the action of gastric 

 juice on native proteins. If the action is very prolonged, polypeptides 

 and amino-acids are split off from the peptones, but in the usual 

 short stay of food in the stomach very little of these ultimate cleavage 

 products is found there. 



They are soluble in water, are not coagulated by heat, and are 

 not precipitated by nitric apid, copper sulphate, ammonium sulphate, 

 and a number of other precipitants of proteins. They are precipi- 

 tated but not coagulated by alcohol. They are also precipitated by 

 tannin, picric acid, potassio-mercuric iodide, phospho-molybdic acid, 

 and phospho-tungstic acid. They give the biuret reaction (rose-red, 

 with a trace of copper sulphate and caustic potash or soda) and are 

 readily diffusible through animal membranes. 



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

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

 products. The protein envelopes of the fat globules are dissolved, and 

 the solid fats are melted. According to some, gastric juice contains 

 a fat-spliting ferment in small quantities which acts like the steapsin 

 of pancreatic juice ; but this action if present is very slight. Starch 

 is unaffected ; but cane sugar is inverted. The inversion of cane 

 sugar is due to the hydrochloric acid of the juice, and is frequently 

 assisted by inverting ferments contained in the vegetable food 

 swallowed. The stomach does not digest itself, because it forms an 

 antipepsin ; similarly in the intestine an antitrypsin is formed. The 

 formation of anti-bodies will be treated under the heading Immunity. 

 (See BLOOD.) 



