34 PRACTICAL PHYSIOLOGY. [V. 



fleeted light, it is much darker, it looks almost black — but by 

 transmitted light it is transparent. Test this by looking as in 2 

 (a.) at printed matter. 



(h.) To C add a watery solution of taurocholate of soda. Test 

 the transparency of the mixture. In 2, the haemoglobin is still 

 witliin the blood corpuscles. In the others — 3 (r/.), {b.) — it is 

 dissolved out, and in solution. 



4. Specific Gravity of Blood. — {a.) Make a number of solutions of sulphate 

 of soda, varying in sp. gr. from i. 050-1. 075. At least twenty sej)arate solu- 

 tions are required, each with a definite sp. gr. Pour a small quantity of the 

 solutions into small glass thimbles. A thin glass tube is drawn out in a gas- 

 flame to form a capillary tube, which is bent at a right angle, and closed 

 above with a small caoutchouc cap. A drop of blood is obtained from a 

 finger, and by pressing lightly on the caoutchouc cap a quantity of the 

 freshly-shed blood is drawn up into the capillary part of the tube. The tip of 

 the fine capillary tube is at once immersed in one of the solutions of sodic sul- 

 phate, and a drop of the blood expressed into the saline solution, and it is noted 

 whether it sinks or floats. The operation is repeated with other solutions until 

 one is found in which the blood neither sinks nor floats. The sp. gr. of blood 

 varies from 1045-1075, the average sp. gr. being 1056-1059. 



(b.) Haycraft's Method.— Make a mixture of toluol (s. g. 800) and benzyl 

 chloride (s. g. iioo) to obtain a fluid with a s. g. of 1070. Label this A. 

 Make another with the s. g. 1025. Label this B. 



Method. — With a pipette place a measured quantity of A in a warm cylin- 

 drical glass. Add a drop of the blood. It will float ; now add B until the 

 blood neither floats nor sinks. 



Suppose 1.5 cc. of B has been added to i cc. of A, then 



I cc. of A (1070) =1,070 

 1,5. 1.5 cc. of B (1025)= 1,537 



2.5 cc 2,607 



Divide this by the total volume 2.5 cc. = 1043, the s. g. of the blood. 



5. Action of a SaHne Solution. 



{a.) To 2 cc. of defibrinated blood in a test-tube (D) add 5 

 volumes of a 10 per cent, solution of sodium chloride. It changes to 

 a very bright, florid, brick-red colour. Compare its colour with that 

 in A, B, and C. It is opaque. 



6. Red Corpuscles.— Add to defibrinated ox blood ^or, better, dog's blood), 

 20 volumes of a dilute solution of NaCl C5-2 per cent.). The red corpuscles 

 subside, and the supernatant fluid can be poured off. Wash the corpuscles 

 several times in this way. They will be required for the preparation of 

 haemoglobin (p. 65). 



7. Hgemoglobin does not Dialyse. 



(a.) Place a watery solution of defibrinated blood in a dialyser 

 (a bulb form or a parchment tube), and suspend it in a large 

 vessel of distilled water. Test the dialyser beforehand to see 



