462 PEACTICAL PHYSIOLOGY 



make a mixing chamber. By attaching a piece of indiarubber tubing to the 

 tube, blood is sucked up to the mark 100, clotting being retarded by first of 

 all drawing some cedar oil through the tubes. The tubes are then placed in 

 a holder, the ends being closed by small metal plates held in position by a 

 spring, and rotated on a centrifuge until the corpuscles have been thrown 

 down to a certain mark, which is then noted. After cleaning, blood from 

 the same source is again sucked up to the mark 100 and then an equal volume 

 of some solution. The two are thoroughly mixed in the mixing chamber by 

 means of a fine wire and the instrument again rotated. If the solution is 

 isotonic with the blood serum the corpuscles will stand at the same level as 

 before, if it be hypotonic they will stand at a higher level, if hypertonic, at 

 a lower. It will be seen that by this method we can readily ascertain, in a 

 series of solutions of unknown osmotic pressures, whether one of them is 

 isotonic with the blood serum. 



The haemoglobin may also be caused to leave the corpuscle by bringing 

 about an alteration in the permeability of the envelope. Such an alteration 

 may be brought about in a variety of ways, some of which may be styled 

 physical, such as heating, freezing or shaking the blood ; others, as purely 

 chemical, such as the addition of ether and other fat solvents, saponin, bile 

 salts, acids and alkalies ; and others as bio-chemical, such as the addition of 

 immune serum. 



In the present state of our knowledge it is impossible to say in every case 

 definitely what the alteration in permeability is due to, but some very important 

 facts are known. 



Physical Laking. EXPERIMENT V. 1. Place some blood in a test tube and 

 keep at 60 C. for a few minutes. The blood becomes laked. 



2. Repeatedly freeze and thaw some blood and then dilute with some isotonic 

 saline. Note the evidence of laking. 



Chemical Laking. 



3. Place some blood in four test tubes ; to one add some ether, to another 

 some 3 per cent, saponin solution, to a third a solution of sodium taurocholate 

 in isotonic saline, and to the fourth some acetic acid. Laking occurs in all 

 cases. 



4. To another test tube containing 1 c.c. of blood add 3 c.c. of a 2 per cent, 

 solution of urea. Laking soon occurs. Since this strength of urea solution 

 has practically the same osmotic pressure as '9 per cent. NaCl, it is of further 

 interest to see whether its laking influence is due to its having, like the 

 above-mentioned chemicals, a damaging effect on the corpuscular envelope. 

 This question can be settled by repeating the above experiment with a solution 

 of 0'9 per cent. NaCl containing 2 per cent, of urea. It will be found that 

 no laking occurs thus showing that, unlike bile salts and saponin, the urea 

 does not damage the envelope. The reason why laking occurs with the pure 

 urea solution must therefore be that the urea molecule penetrates the corpus- 

 cular envelope very readily, perhaps as readily as water itself does. 



A considerable amount of work has been done on saponin laking, the most 

 important outcome of which has been to show that the haemolytic effect of 

 this drug can be antidoted by something (probably lecithin or cholesterol) 

 contained in normal blood serum. To demonstrate this effect it is of course 



