2l6 MICROMETRY AND BLOOD PREPARATIONS 



An accurate urinometer will suffice to determine the specific gravity. Drops of 

 blood from the cholera patient are deposited at the center of the surface of the fluid 

 in the bottles from a capillary pipette. If the specific gravity of the blood is 1062 

 at least a liter of saline or sodium bicarbonate solution is needed. If 1066 at least 

 2 liters. Formerly he estimated the indications by blood-pressure considering a 

 pressure of 80 in Europeans or of 70 in natives as indicating intravenous injections. 



TESTS FOR AGGLUTINATION AND HAEMOLYSIS OF THE RED CELLS 

 (TRANSFUSION) 



In the selection of a donor for blood for transfusion it is always 

 necessary to try his red cells against the serum of the recipient as well 

 as the patient's red cells against the serum of the donor, in order to 

 prove the absence of haemolyzing or agglutinating bodies. 



Certain persons have isohaemolysins in their blood which dissolve the red cells of 

 other persons and in paroxysmal haemoglobinuria autohaemolysins may be present 

 which can destroy the patient's own red cells. This autohaemolysin seems operative 

 only when a low temperature is followed by a high one. When haemoglobinaemia 

 exists the liver converts it into bile pigment, causing bilious stools and jaundice. If 

 one-sixth of the red cells are destroyed hEemoglobinuria results. 



Before transfusing carry out the following tests: 



From a vein take about i c.c. of blood in a centrifuge tube containing i % of sod. 

 citrate salt solution; then shift the stopper of the blood system to a dry centrifuge 

 tube and draw into it about 3 or 4 c.c. of blood. Throw down the citrated blood, 

 pipette off the supernatant fluid and wash the sediment with normal saline. 



Again pipette off the saline after centrifuging and make a 10% emulsion of the red- 

 cell sediment in normal saline. 



Centrifuge the coagulated blood in the other tube and collect the serum which 

 separates from the clot. 



Carry out these procedures for both donor and recipient. 



Tests: i. In a small test-tube deposit i drop of the donor's 10% red-cell emulsion 

 and then add 4 drops of the recipient's serum. 



2. Treat similarly i drop of the recipient's red-cell emulsion with 4 drops of the 

 donor's serum. 



3. Treat i drop of donor's red-cell emulsion with 4 drops of his serum. 



4. Treat i drop of recipient's red-cell emulsion with 4 drops of his serum. Finally 

 add i c.c. of salt solution to each of the four tubes, shake gently and place in incubator 

 for two hours. 



Tests 3 and 4 should fail to show either agglutination or haemolysins. 

 Some prefer to keep the tubes over night in ice-box after the preliminary examina- 

 tion following incubation. 



OCCULT BLOOD 



When the presence of blood cannot be recognized by macroscopical 

 or microscopical methods (occult blood) we must resort to spectro- 



