222 AGRICULTURAL CHEMISTRY 



egg albumin with pepsin. 5 grams of commercial pepsin are dis- 

 solved in i liter of water containing 5 drops HC1. This artificial 

 pepsin solution represents the solvent power of gastric juice upon 

 proteid substances. The white of a hard boiled egg is put into a 

 flask, and 250 cc. pepsin solution added ; the flask is then placed in 

 a water-bath which is kept at a temperature of 38 C. for four or 

 five hours. 



Questions. ( I ) What action did the pepsin have on the egg 

 albumin and what was produced? (2) What was the result when 

 heat was applied in test No. I, and how does this compare with the 

 result when egg albumin was similarly treated ? (3) What effect 

 did tannic acid and alum have upon the pepsin solution and what 

 did they produce? (4) What was the result when alcohol was 

 added? (5) What are peptones ? (6) What does this experiment 

 show in regard to some of the properties of peptones? 



304. Insoluble Proteids. The insoluble proteids are 

 present in plant and animal bodies in larger amounts 

 than are any of the other proteids, and include a large 

 number of similar though chemically distinct bodies. 

 Muscular tissue is composed largely of insoluble proteids. 

 In seeds, the term gluten is frequently applied to this 

 class of compounds which is a mixture of two or more 

 insoluble proteids. Wheat gluten for example is com- 

 posed of gliadin and glutenin. Gliadin is a glue-like body 

 which binds together the flour particles, and in bread- 

 making, enables the gas to be retained in the dough. 

 Glutenin is a fine, gray material which unites mechanically 

 with the gliadin to form gluten. An excess of gliadin 

 produces a soft gluten. 



As a class, the insoluble proteids are not soluble in 

 water or dilute salt solutions, but are soluble in dilute 

 acids and alkalies. They all undergo the peptonizing 



