PHYSICAL PROPERTIES OF THE BLOOD. 



(2.) Reaction. The reaction is alkaline, owing to the presence of 

 disodic phosphate, Na 2 ,H,P0 4 (Maly). After blood is shed, its 

 alkalinity rapidly diminishes, and this occurs more rapidly the greater 

 the alkalinity of the blood. This is due to the formation of an acid, in 

 which, perhaps, the coloured corpuscles take part, owing to the decom- 

 position of their colouring-matter. A high temperature and the addi- 

 tion of an alkali favour the formation of the acid (N. Zuntz). 



The alkalinity is less in persons suffering from anaemia, cachectic conditions, 

 and chronic rheumatism (Lupine). After the prolonged use of soda, the alkali 

 in the ash of blood is increased (Dubelir). 



Methods. Owing to the colour of the blood we cannot employ ordinary litmus 

 paper to test its reaction. One or other of the following methods may be used : 

 (1.) Moisten a strip of glazed red litmus paper with solution of common salt, and 

 dip it quickly into the blood, or allow a drop of blood to fall on the paper, and 

 rapidly wipe it off before its colouring-matter has time to penetrate and tinge the 

 paper (Zuntz). (2.) Klihne made a small cup of parchment paper which was 

 placed in water in a watch-glass. The colourless diffusate was afterwards tested 

 with litmus paper. (3.) Liebreich used thin plates of plaster-of-Paris of a per- 

 fectly neutral reaction. These are dried, and afterwards moistened with a neutral 

 solution of litmus. When a drop of blood is placed upon the porous plate, the 

 fluid part of the blood passes into it, while the corpuscles remain at the surface. 

 The corpuscles are washed off with water, and the altered colour of the litmus- 

 stained slab is apparent. [(4.) Sch'afer uses dry faintly-reddened glazed litmus 

 paper, and on it is placed a drop of blood, which is wiped off after a few seconds. 

 The place where the blood rested is indicated by a well-defined blue patch upon 

 a red or violet ground.] 



The alkaline reaction of blood is diminished : (a) By great muscular exertion, 

 owing to the formation of a large amount of acid in the muscles ; (|3) during 

 coagulation ; (y) in old blood, or blood dissolved by water from old blood- stains, 

 such blood being usually acid. Fresh cruor has a stronger alkaline reaction than 

 serum. 



(3.) Odour. Blood emits a peculiar odour (Halitus sanguinis), which 

 differs in animals and man. 



It depends upon the presence of volatile fatty acids. If concentrated sulphuric 

 acid be added to blood, whereby the volatile fatty acids are set free from their com- 

 binations with alkalies, the characteristic odour becomes much more perceptible 

 (Barruel). 



(4.) Taste. Blood has a saline taste, depending upon the salts dis- 

 solved in the fluid of the blood. 



(5.) Specific Gravity. The specific gravity is 1,055 (extreme limits 

 1,045-1,075); in women and young persons it is somewhat less. 

 The specific gravity of the blood-corpuscles is 1,105, that of the 

 plasma 1,027. Hence, the corpuscles tend to sink. 



The specific gravity of the red blood-corpuscles is estimated by allowing the 

 corpuscles to subside to the bottom (which occurs most readily in the blood of 

 the horse) ; but it is more correctly estimated by placing the blood in a tall 

 cylindrical vessel, and setting the latter in the radius of the revolving 

 disc of a centrifugal apparatus, the base of the cylinder being directed out- 

 wards. The drinking of water and hunger diminish the specific gravity tern- 



