CHAPTER XII. 



BLOOD. 



BLOOD is composed of four types of form-elements (erythrocytes 

 or red blood corpuscles, leucocytes or white blood corpuscles, blood 

 plates or plaques and blood dust or haemoconien) held in suspen- 

 sion in a fluid called blood plasma. These form-elements compose 

 about 60 per cent of the blood, by weight. Ordinarily blood is a 

 dark red, opaque fluid due to the presence of the red blood corpus- 

 cles, but through the action of certain substances such as water, 

 ether or chloroform it may be rendered transparent. Blood so 

 altered is said to be lakcd. The laking process is simply a liberation 

 of the haemoglobin from the stroma of the red blood corpuscle. 

 Normal blood is alkaline in reaction 1 to litmus, the alkalinity being 

 due principally to sodium carbonate and phosphate. The specific 

 gravity of the blood of adults ordinarily varies between 1.045 an d 

 1.075. It varies somewhat with the sex, the blood of males hav- 

 ing a rather higher specific gravity than that of females of the 

 same species. Under pathological conditions also the density of 

 the blood may be very greatly altered. The freezing-point (A) of 

 normal blood is about 0.56 C. Variations between 0.51 

 and 0.62 C. may be due entirely to dietary conditions, but if any 

 marked variation is noted it can in most cases be traced to a dis- 

 ordered kidney function. The total amount of blood in the body 

 has been variously estimated at from one-twelfth to one- fourteenth 

 of the body weight. Perhaps 1/13.5 is the most satisfactory figure. 



Among the most important constituents of blood plasma are the 

 four protein bodies, fibrinogen, nude o protein, serum globulin (eu- 

 globulin and pseudo-globulin) and serum albumin. Plasma con- 

 tains about 8.2 per cent of solids of which the protein constituents 

 named above constitute approximately 84 per cent and the inor- 

 ganic constituents (mainly chlorides, phosphates and carbonates) 

 approximately 10 per cent. Among the inorganic 'constituents 

 sodium chloride predominates. To prevent coagulation, blood 

 plasma is ordinarily studied in the form of an oxalated or salted 



1 Recently it has been shown by physico-chemical methods that the blood 

 is in reality neutral in reaction. 



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