102 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



(0.1 per cent.) acids without dissolving, but which is soluble in the caustic 

 alkalies, and may be precipitated by neutralization. 



Alkali albumen, like other albuminous bodies, is also precipitated 

 from its solutions by metallic salts. With alcohol no precipitate is 

 yielded, and alkali albumen is said to contain no sulphur, the sulphur of 

 the albumen from which it is made being removed by the alkali in the 

 process of conversion. It therefore differs from acid albumen and from 

 casein, which contains sulphur. 



Alkali albumen or albuminate is present in all young cells, in blood- 

 corpuscles and blood-serum, in muscle, pancreas, nerves, crystalline lens, 

 and cornea. It would seem that alkali albuminate may exist in various 

 forms, judging by the difference in effect produced on polarized light by 

 alkali albumen produced from different sources. Thus, alkali albumen 

 produced from serum-albumen has a laevo-rotatorj* power of — 86° ; from 

 egg-albumen, of — 47°, and if prepared from coagulated egg-albumen it 

 may be as high as — 58.8°. 



Casein is a form of alkali albuminate which is present in milk. It 

 yields potassium sulphide when left to stand with liquor potassae, and 

 still more quickly when heated with it. It may be prepared from milk by 

 shaking the milk with caustic potash and ether, removing the ether and 

 precipitating the albuminate with acetic acid, and washing the coagulum 

 with water, alcohol, and ether. The other properties of casein will be 

 further studied under the subject of Milk. 



Alkali albumen, therefore, differs from acid albumens in its not being 

 precipitated on neutralization if alkaline phosphates be present ; by its 

 being precipitated by magnesium sulphate in substance in cold solution, 

 but in not being coagulated when boiled in lime-water; and it contains no 

 sulphur. 



T Coagulated Proteids. — It has already been seen that the action 

 of heat on solutions of egg- and serum-albumen, globulins, or on fibrin 

 when suspended in water, or dissolved in saline solutions, serves to 

 coagulate them and to convert them into an insoluble form. Absolute 

 alcohol produces a similar effect on the same bodies ; coagulated proteids 

 are insoluble in water, dilute acids and alkalies and neutral saline solu- 

 tions, and, although they are soluble in the strong mineral acids, their 

 solubility is dependent upon the fact that through the action of the acid 

 they are converted into derived albumens. They are readily converted 

 into peptones through the action of the different digestive juices (gastric 

 and pancreatic juices). When freshly formed they are white, flocculent, or 

 cheesy masses which, under the microscope, are entirely amorphous; 

 they hold water and salt solutions with great tenacity. Their chemical 

 characteristics have been very little studied. 



VI. Amyloid Substances oh Laudacein.— This is a substance which 



