70 THE CIRCULATING LIQUIDS OF THE BODY 



the total length of the wire being 100. Then resistance of A : resistance 

 of B:: 49-0: 51-0, i.e., resistance of A = resistance of B. 



(b) Fill A with defibrinated blood, keeping B filled with NaCl solu- 

 tion, and repeat the measurement. The slider must now be moved 

 much farther away from the zero of the scale. Suppose the minimum 

 sound is obtained with the slider at 70-0. Then resistance of blood = 



3 x resistance of the NaCl solution. 

 7 49 



(c) Compare in the same way the resistance of serum with that of 

 the NaCl solution. It will be found much less than that of the blood. 



(d) Centrifugalize some of the blood for as long as is convenient, and 

 compare the resistance of the blood from the top of the tubes and from 

 the bottom of the tubes with that of the NaCl solution. The resistance 

 of the blood from the bottom of the tubes will be found much greater 

 than that of the blood from the top. 



13. Opacity of Blood. Smear a little fresh blood on a glass slide, and 

 hold the slide above some printed matter. It will not be possible to 

 read it, because the light is reflected from the corpuscles in all directions, 

 and little of it passes through. 



14. Laking of Blood by Chemical and Physical Agents. (i) Put a 

 little fresh blood into three test-tubes, A, B, and C. Dilute A with an 

 equal volume, B with two volumes, and C with three volumes, of dis- 

 tilled water, and repeat experiment 9. The print can now be read 

 probably through a layer of A, but certainly through B and C, since 

 the haemoglobin is dissolved out of the corpuscles by the water and 

 goes into solution, the blood becoming transparent or laked. That the 

 difference is not due merely to dilution can be shown by putting an 

 equal quantity of blood in two test-tubes, and gradually diluting one 

 with distilled water and the other, with a 0*9 per cent, solution of 

 sodium chloride, which does not dissolve out the haemoglobin. Print 

 can be read through the first with a smaller degree of dilution than 

 through the second. Examine the laked blood with the microscope 

 for the ' ghosts/ or shadows of the red corpuscles. The addition of a 

 drop or two of methylene blue will render them somewhat more distinct. 



(2) Heat a little dog's or ox blood in a test-tube immersed in a water- 

 bath. Put a thermometer in the test-tube, taking care that there is 

 enough blood to cover the bulb. Keep the temperature about 60 C. 

 In a few minutes the blood becomes dark and laking occurs. 



(3) (a) Put a little blood into each of four test-tubes. To one add a 

 little ether, to another a little chloroform, to the third dilute acetic 

 acid in 0-9 per cent. NaCl, and to the fourth a dilute solution of bile 

 salts (or of sodium taurocholate) in 0-9 per cent. NaCl solution. Laking 

 occurs in all. 



(b) To 5 c.c. of blood add 0*5 c.c. of a 3 per cent, solution of saponin 

 in 0-9 per cent. NaCl solution, and put the mixture at 40 C. Laking 

 soon occurs. 



(c) Using a 10 per cent, dilution of blood (blood to which nine volumes 

 of NaCl solution have been added) or a 5 per cent, suspension of washed 

 corpuscles in NaCl solution (i.e., a suspension of corpuscles which have 

 been washed free from serum by being repeatedly mixed with NaCl 

 solution and centrifugalized), determine the minimum dose of 0-3 per 

 cent, saponin solution which will just cause complete laking. Keep the 

 tubes at about 40 C., and observe them from time to time. Now add 

 to some of the 10 per cent, dilution or the 5 per cent, suspension of blood 

 an equal volume of serum from the same kind of blood, and repeat the 

 determination of the minimum dose of saponin necessary for laking. 



