THE BLOOD. 231 



3. Odor. When freshly drawn the blood possesses a peculiar 

 characteristic odor which has been nttribntfti tip tb^J p rpg ence of q. 

 volatile fatty acid in combination with an alkaline Dase. I'he^in- 

 tensity of the "'odor mayHfre Tncreaself ByTfie~*a^^ 



sulphuric acid, by means of which the volatile acid is set free. 



4. Specific Gravity. The specific gravity of blood lies within 

 the limits of 1.051 and 1.059, averaging in man 1.056 and in woman 

 1.053. Normally, variations from these values are only temporary and 

 are connected with variations in physiologic processes. The specific 

 gravity is diminished by the ingestion of liquids and abstinence from 

 solid food. It is increased by abstinence from liquids, by the inges- 

 tion of dry food, and by the elimination of large quantities of water 

 by the lungs, skin, and kidneys. 



5. Alkalinity. The reaction of the blood is alkaline from the 

 presence of the disodium phosphate (Na 2 HPO 4 ) and the sodium car- 

 bonate, Na 2 CO 3 . The alkalinity can be readily shown by allowing 

 the blood to remain for a few seconds on slightly reddened glazed 

 litmus paper. On washing off the blood a distinct blue color pre- 

 sents itself against a red or violet background. The alkalinity varies 

 within narrow limits in consequence of variations in physiologic 

 processes. It is increased in the early stages of digestion and de- 

 creased after the absorption of the hydrochloric acid and the pep- 

 tones, and decreased after muscular exercise in consequence of the 

 increased production and absorption of acids. According to v. Jaksch, 

 the alkalinity corresponds to from 260 to 300 milligrams of sodium 

 hydrate, NaOH, for every 100 c.c. of blood; according to Lowy, 

 from 300 to 325 milligrams. The hitherto unavoidable error in these 

 estimates is about 30 milligrams. 



6. Temperature. The temperature varies from 36.78 C. 

 (98.2 F.) in the superior vena cava to 39.7 0^103.4 F.) in the 

 hepatic vein, the mean being about 38 C. (100 F.). 



Coagulation of the Blood. Within a few minutes after the 

 blood is withdrawn from the vessels of a living animal it begins to 

 lose its fluidity, becomes somewhat viscid, and if left undisturbed 

 passes rapidly into a semi-solid or jelly-like state. To this change 

 in the physical condition of the blood the term coagulation has been 

 applied. The blood, during the progress of coagulation, not only 

 assumes the shape of the vessel in which it is contained, but becomes 

 so firmly adherent to its walls that it may be inverted without the 

 coagulum becoming dislodged. If a portion of such a jelly-like mass 

 be examined microscopically, it will be found to be penetrated in all 

 directions by a felt-work of extremely fine delicate fibrils, which, 

 having made their appearance before the corpuscles had time to 

 settle to the bottom of the fluid, have entangled them in the meshes 



