PRACTICAL EXERCISES 65 



of the corpuscles, or the resistance of the weakest corpuscles. Repeat 

 with blood which has stood at room, temperature for twelve to 

 twenty-four hours. For clinical purposes tubes, each containing 

 5 c.c. of salt solution, may be used. A single drop of blood can then 

 be distributed between the tubes with a fine pipette or a glass rod, 

 beginning with the most concentrated solution, and passing down 

 to the less concentrated. The blood must be distributed rapidly 

 before coagulation occurs. Only such concentrations of the salt 

 solution as are known to correspond to the possible variations of the 

 osmotic resistance for any particular disease or for any particular 

 variety of blood need be employed. 



14. Blood-pigment (i) Preparation of Haemoglobin Crystals. (a) 

 To a little dog's blood in a narrow test-tube add its own volume or 

 twice its volume of chloroform. Invert the tube ten or twelve times 

 so as to allow the chloroform to act on the blood, but avoid violent 

 shaking. When the tube is now allowed to stand for a few minutes 

 the laked blood all rises to the top. Remove a little of the layer 

 of blood without taking with it any of the chloroform layer, and 

 examine the oxyhaemoglobin crystals with the microscope. They 

 form long rhombic prisms and needles (Fig. 8, p. 45). 



(b) Add a little crude saponin to dog's blood in a test-tube. Shake 



FIG. 14. DIRECT VISION SPECTROSCOPE OF SIMPLE TYPE. 

 A, slot in which a pin on the eyepiece C slides in focussing the spectrum; 

 B, milled head, by the rotation of which the slit is narrowed or widened. 



up well, and allow it to stand till the colour becomes dark. Then 

 shake vigorously, and a mass of haemoglobin crystals will be formed. 



(c) Put a small drop of guinea-pig's blood on a slide. Mix with a 

 drop of Canada balsam and cover. Tetrahedral crystals of oxy- 

 haemoglobin will form after a time. The slide may be kept. 



(2) Spectroscopic Examination of Haemoglobin and its Derivatives. 

 (a) With a small, direct-vision spectroscope look at a bright part of 

 the sky or a white cloud. Focus by pulling out or pushing in the eye- 

 piece until the numerous fine dark lines (Fraunhofer's lines), running 

 vertically across the spectrum, are seen. Narrow the slit by moving 

 the milled edge till the lines are as sharp as they can be made. Note 

 especially the line D in the orange, the lines E and b in the green, 

 and F in the blue. Always hold the spectroscope so that the red is 

 at the left of the field. Now dip an iron or platinum wire with a 

 loop on the end of it into water, and then into some common salt or 

 sodium carbonate, and fasten or hold it in the flame of a fishtail 

 burner. On examining the flame with the spectroscope, a bright 

 yellow line will be seen occupying the position of the dark line D in 

 the solar spectrum. This is a convenient line of reference in the 

 spectrum, and in studying the spectra of haemoglobin and its deri- 

 vatives, the position of the absorption bands with regard to the D 

 line should always be noted. The dark lines in the solar spectrum 



5 



