PROTEIDS. 419 



fiask, add solution C, shake well, and place the flask in a water-bath, or 

 thermostat, kept at a temperature of 38 to 40 C. (100 to 104 F.) for six 

 hours, and shake it gently every fifteen minutes. If, at the expiration of that 

 time, the albumin should have disappeared, leaving at most only a few, thin, 

 insoluble flakes, then the dissolving power of the pepsin examined is not less 

 than 3000. 



The relative proteolytic power of pepsin, stronger or weaker than that de- 

 scribed above, may be determined by ascertaining, through repeated trials, how 

 much of solution B made up to 100 c.c. with solution A will be required to 

 dissolve 10 grammes of albumin under the conditions given above. 



Pancreatin, U. S. P. This preparation is a mixture of the 

 enzymes existing in the pancreas of warm-blooded animals, and is 

 usually obtained from the fresh pancreas of the hog. It is a 

 yellowish, or grayish, almost odorless powder, soluble in water, 

 insoluble in alcohol. It has the power to digest proteids, and to 

 convert starch into sugar. 



If there be added to 100 c.c. of water contained in a flask, 0.28 gramme of 

 pancreatin and 1.5 gramme of sodium bicarbonate, and afterward 400 c.c. of 

 fresh cow's milk, previously heated to 38 C. (100 F.), and if this mixture be 

 maintained at the same temperature for thirty minutes, the milk should be so 

 completely peptonized that, if a small portion of it be transferred to a test-tube 

 and mixed with some nitric acid, no coagulation should occur. 



Gelatinoids. To this group belong a number of substances 

 occurring in bones, skins, horns, hair, nails, feathers, etc., and 

 having generally the property of forming a jelly with water. The 

 organic matter in bones, usually called ossein, contains, besides an 

 albuminous substance, the two gelatinoids collagen and gelatin, an 

 impure mixture of which forms common glue. 



QUESTIONS. 501. To which class of substances is the term proteids applied, 

 and which elements enter into their composition ? 502. By what processes are 

 proteids formed in nature, and where do they occur? 503. State the general 

 properties of proteids. 504. How are proteids acted upon by heat, nitric acid, 

 and Millon's reagent? 505. Into which groups may proteids be classified, and 

 how do they differ from each other? 506. Mention some native albumins; 

 state where they are found, and by what tests they are characterized ? 507. 

 How may blood-fibrin be obtained and what are its properties ? 508. State 

 formation and characteristic properties of peptones. 509. What elements are 

 found in haemoglobin, where does it exist, and what are its characteristic 

 properties ? 510. What is pepsin, and how does it act upon proteids ? 



