20 TEXT-BOOK OF PHYSIOLOGY 



This is also known as Piotrowski's test: As this same color is de- 

 veloped with the substance biuret, it is also known as the biuret 

 reaction. Biuret is formed by heating urea to i8oC and driving off 

 ammonia. 



Precipitation Tests. Proteins in solution may be precipitated by 

 nitric acid, acetic acid and potassium ferrocyanid, picric acid, copper 

 sulphate, tannin, alcohol, etc. As stated in a foregoing paragraph, certain 

 of the proteins, e.g., fibrinogen, caseinogen and myosinogen, will undergo, 

 by the action of an animal ferment a change of state by virtue of which 

 they become solid. To this process the term ferment coagulation is applied. 

 The solidification of proteins by the action of heat is designated heat 

 coagulation. 



INORGANIC CONSTITUENTS 



The inorganic compounds and mineral constituents obtained from the 

 solids and fluids of the body are very numerous, and, in some instances, 

 quite abundant. Though many of the compounds thus obtained are 

 undoubtedly derivatives of the tissues and necessary to their physical and 

 physiologic activity, others, in all probability, are decomposition products, 

 or transitory constituents introduced with the food. Of the inorganic 

 compounds, .the following are the most important : 

 WATER. 



Water is the most important of the inorganic constituents, as it is in- 

 dispensable to life. It is present in all the tissues and fluids without excep- 

 tion, varying from 99 per cent, in the saliva to 80 per cent, in the blood, 75 

 per cent, in the muscles to 2 per cent, in the enamel of the teeth. The total 

 quantity contained in a body weighing 75 kilograms (165 pounds) is 52.5 

 kilograms (115 pounds). Much of the water exists in a free condition, and 

 forms the chief part of the fluids, giving to them their characteristic degree of 

 fluidity. Possessing the capability of holding in solution a large number of 

 inorganic as well as some organic compounds, and being at the same time 

 diffusible, it renders an interchange of materials between all portions of the 

 body possible. It aids in the absorption of new material into the blood and 

 tissues, and at the same time it transfers waste products from the tissues to 

 the blood, from which they are finally eliminated, along with the water in 

 which they are dissolved. A portion of the water is chemically combined 

 with other tissue constituents and gives to the tissues their characteristic- 

 physical properties. The consistency, elasticity, and pliability are, to a 

 large extent, conditioned by the amount of water they contain. The total 

 quantity of water eliminated by the kidneys, lungs, and skin amounts to 

 about 3 kilograms (6J pounds) daily. 

 CALCIUM COMPOUNDS. 



Calcium phosphate, Ca 3 (PO 4 ) 2 , has a very extensive distribution 

 throughout the body. It exists largely in the bones, teeth, and to a slight ex- 

 tent in cartilage, blood, and other tissues. Milk contains 0.27 per cent. 

 The solidity of the bones and teeth is almost entirely due to the presence of 

 this salt, and is, therefore, to be regarded as necessary to their structure. 

 It enters into chemic union with the organic matter, as shown by the fact 

 that it cannot be separated from it except by chemic means, such as immer- 



