PRACTICAL EXERCISES 73 



laking in either G or H, or if there is laking it may be greater in G than 

 in H. The amboceptor has been removed from serum S by the rabbit's 

 corpuscles. Add o-i c.c. of this ' inactivated ' serum to the balance 

 of D, D', and E, E' (left from 6). Laking will occur because the serum S 

 contains complement, and the heated serum added in (6) to these tubes 

 contains amboceptor. Wash the rabbit's corpuscles which have been 

 treated with ox serum at o C. with cooled sodium chloride solution. 

 Add to them some of serum S (that from the top of tube H will do if 

 no more is left), and put at 40 C. Laking will occur, showing that the 

 amboceptor was fixed by the rabbit's corpuscles at o C. To a further 

 portion of the washed rabbit's corpuscles which were treated with ox 

 serum at o C. add normal rabbit's serum, and put at 40 C. If laking 

 occurs it is because the rabbit's serum contains complement. 



Dog's serum may be used instead of ox serum for experiment (8). 



1 6. Osmotic Resistance of the Coloured Corpuscles. Fill a burette 

 with a I per cent, solution of sodium chloride and another with dis- 

 tilled water. Take a series of ten test-tubes and run into the first 

 6 c.c. of the NaCl solution, into the second 5-8 c.c., into the third 

 5-6 c.c., and so on, always making a difference of 0-2 c.c. between 

 successive test-tubes. From the other burette run in enough distilled 

 water to make up 10 c.c. of solution in each tube that is, 4 c.c. of dis- 

 tilled water for the first tube, 4-2 c.c. for the second, and so on. Shake 

 up. The tubes now contain a series of solutions of salt differing in 

 strength by 0-02 per cent, in successive tubes, the strongest being 0-6 

 per cent., and the weakest 0-42 per cent. Number the tubes i to 10, 

 beginning with the strongest solution. Put into each tube one drop of 

 perfectly fresh blood. Shake moderately so as to mix the blood and 

 salt solution, and allow the tubes to stand for ten to thirty minutes. 

 Observe the colour of the clear liquid above the sediment of corpuscles. 

 Determine in which tube the first tinge of haemoglobin appears. The 

 next higher concentration of the salt solution is that in which all the 

 corpuscles are just able to retain their haemoglobin, and is a measure of 

 the minimum osmotic resistance 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 dis- 

 tributed 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. 



17. 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. 14, p. 52). 



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

 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 



