ELEMENTARY CHEMICAL PHYSIOLOGY 239 



CHAPTER XI 

 BLOOD 



To the unaided eye ordinary blood appears to be a homogeneous 

 red fluid, but examination with the microscope shows that the red 

 colour is confined to certain formed elements, the red corpuscles, 

 suspended in a faintly yellow fluid, the plasma. 



EXPERIMENT, (a) Note with the aid of a microscope the dis- 

 position of the colouring matter, the haemoglobin, in the red blood 

 corpuscles or erythrocytes. (6) Undiluted blood appears to be an 

 opaque fluid. Take two test tubes, place 5 c.c. water in one and 

 an equal volume of 0-9 per cent, sodium chloride solution in the 

 other and then add to each a drop of whipped blood. The pigment 

 dissolves out of the corpuscles in the first, the mixture becoming 

 transparent (laked) but not in the second. Confirm by the micro- 

 scope, (c) Test the Specific Gravity. Take mixtures of chloroform 

 and benzene ranging from a specific gravity of 1,040 to 1,070, 

 or a series of solutions of sodium sulphate of similar range of 

 specific gravities. Introduce the blood to be tested (a drop of 

 blood from the finger) below the surface of the fluid by means of a 

 capillary tube. Note whether the drop floats, sinks, or remains 

 suspended. Note the specific gravity of the solution in which the 

 drop remains suspended, (d) The reaction of the blood may be 

 determined by placing a freshly -drawn drop of blood on red glazed 

 litmus paper, allow it to remain for a few seconds, then wash it 

 off under the tap. 



The Clotting of Blood. When blood is shed it sets at first to a 

 red jelly, after a time this jelly contracts and gradually squeezes 

 out a pale yellow fluid, the serum. 



EXPERIMENT I. Carefully sterilise a needle, prick the finger, and 

 draw some blood into a fine capillary tube. Place aside and examine 

 under the microscope at the end of the lesson. 



In order to study the nature of the processes involved in the coagulation of 

 blood, it is essential to stop clotting from taking place. This can be done in 

 several ways, such as receiving blood into certain neutral salts (e.g. quarter 

 volume of magnesium sulphate, equal volume of sodium sulphate), or on to 

 a soluble citrate, oxalate or fluoride. Upon standing, the corpuscles will 

 gradually sink, and the supernatant plasma can be pipetted off, or, preferably, 

 the mixture can be centrifugalised. This plasma is called "salted" or 

 " oxalated," or " fluoride " plasma and so on. 



EXPERIMENT II. Take about 5 c.c. of salted plasma in each of 

 three large test tubes, a, 6 and c, and then dilute each by the addi- 

 tion of 5 volumes of water. Leave a untouched ; to 6 add a few 

 drops of normal serum ; to c a few drops of serum previously heated 

 to 60 C. Place all three tubes in water-bath at 37 to 40 C. a 

 and c clot about the same time, 6 clots more quickly, i.e. addition 

 of normal serum hastens clotting. 



