MILK. 445 



but a mixture of several substances similar in composition and 

 properties. 



Mucus is secreted by the various mucous membranes, and is found 

 in saliva, bile, connective tissues, feces, urine, etc. When pure it 

 forms a clear, translucent or viscid mass ; it contains a substance 

 termed mucin, which swells up in water, and readily dissolves in 

 water containing an alkali ; from these solutions it is precipitated by 

 acetic acid. 



Muscles contain fibrin, albumin, myosin, kreatin, C 4 H 9 N 3 O 2 , 

 sarkin, C 5 H 4 N 4 O, xanthin, C 5 H 4 N 4 O 2 , uric acid, glucose, inosite, 

 lactates, and salts. 



Kreatin, sarkin, and xanthin are substances formed in the organism 

 by oxidation of proteids, and may be looked upon as compound ureas 

 or substances formed as intermediate products of the final conversion 

 of proteids into urea, carbon dioxide, water, etc. These substances 

 may indeed be decomposed artificially in such a manner that urea is 

 produced as one of the products of decomposition. 



Brain consists of so many individual parts that the analysis of it 

 as a whole is of little value, and to separate these parts successfully is 

 a task not yet accomplished. Brain, as a whole, contains cerebrin, 

 lecithin, cholesterin, protagon, and many other substances, some of 

 which are distinguished by the large quantity of phosphorus they 

 contain. 



54. MILK. 



Properties and composition. Milk is the secretion of the mam- 

 mary glands, the presence of which is characteristic of the class of 



QUESTIONS. 521. What three kinds of matter are found as constituents of 

 the animal body, and how can they be determined quantitatively? 522. Men- 

 tion the chief constituents of blood, and state those which predominate in serum 

 and in the corpuscles respectively. 523. What substances cause the clotting 

 of blood, and what explanation can be given? 524. How may blood-stains be 

 recognized? 525. What is the active principle of saliva, and how does it act 

 on starch ? 526. State the composition of gastric juice, and explain its physio- 

 logical action. 527. State the general properties of bile, and mention its chief 

 constituents. 528. Give Gmelin's test for biliary pigments, and Pettenkofer's 

 test for biliary acids. What precautions are necessary in using the latter test? 

 529. What is cholesterin ? State its properties and reactions. 530. Mention 

 the principal constituents of muscles, bone, teeth, and hair. 



