242 PRACTICAL PHYSIOLOGY 



saturation). The globulin is precipitated. Filter and fully saturate 

 (add solid crystals) with (NH 4 ) 2 S0 4 ; a precipitate of albumin results. 



Salts. EXPERIMENT VII. Faintly acidify the serum and boil 

 to coagulate the proteins. Filter. Test the nitrate for : 



(a) chlorides by silver nitrate white precipitate insoluble in 

 nitric acid ; 



(6) phosphates white precipitate on addition of ammoniacal 

 magnesium citrate solution. Filter off this precipitate. Dissolve 

 in nitric acid, and heat with nitro-molybdic acid yellow precipitate ; 



(c) sulphates white precipitate with barium chloride, insoluble 

 in hydrochloric acid. 



In all three tests phosphates are precipitated, but in (a) they are 

 soluble in nitric acid, in (c) they are dissolved by hydrochloric acid 

 (cf. salts of urine). 



The amount of sulphate present is usually very small. This 

 filtrate may also be tested for sugar by Fehling's test. 



Blood Plasma. All the above bodies are present in plasma, which 

 contains one substance in addition, namely, Fibrinogen. This has 

 already been shown (Expt. Ill, d). Plasma, however, does not 

 contain thrombin ; serum does. 



When the function of the blood is remembered it is obvious that 

 there are many bodies other than the above present in both plasma 

 and serum in small quantities. Thus the blood carries the food 

 materials to the tissues, and the products of metabolism away from 

 them. There is, therefore, in addition to ammonia, small quantities 

 of nitrogenous extractives : urea, uric acid, creatinine, xanthine, 

 hypoxanthine, etc. ; of non-nitrogenous extractives, fats, cholesterol, 

 lactic and other organic acids. 



The Leucocytes or White Blood Corpuscles 



These are morphologically the same as other cells, and they 

 contain the same chemical substances. The protoplasm consists 

 mainly of water. The solids consist of various proteins, which 

 chiefly belong to the group of compound proteins (gluco-proteins 

 and nucleo-proteins), and there is also a small amount of albumin 

 and globulin. The protoplasm may also contain such substances 

 as glycogen, fat, mucin, etc., which have either been produced by 

 the activity of the protoplasm, or which are simply deposited in 

 the cell for storage purposes. 



The nucleus seems to consist mainly of nucleo-proteins, nuclein 

 and nucleic acid. The nucleo-protein of the nucleus is said to 

 contain a higher percentage of phosphorus than does that of the 

 protoplasm. 



The Erythrocytes or Red Blood Corpuscles 



Structurally these are said to consist of a stroma containing in its 

 meshes a chromo -protein called Haemoglobin. It is, however, impos- 

 sible to demonstrate this stroma histologically, and some authori- 



