6i2 LABORATORY HINTS 



Centrifuge or let it stand several hours, break off end, and blow out 

 serum when required. 



Use a pipette as for the Wassermann reaction. 



Draw seven volumes of normal saline into pipette. 



Express one volume on each of seven clean slides or one large slide. 



Take one volume of serum to be tested and place on a clean slide. 



Take another volume of serum to be tested and place on a slide 

 with one volume of saline. 



71iis serum is now diluted i in 2. 



Take one volume of this latter, mix with another slide with one 

 volume of saline. 



This is I in 3 dilution. 



Repeat this process through the series excepting the seventh slide, 

 as this last is of normal saline for a control. 



Take a thick emulsion of typhoid bacilli from an agar culture. 



Add one volume of this to each of the slides and mix well. 



Examine under a i-in. objective. 



The reaction is positive if complete agglutination occurs imme- 

 diatelv in the i in 2 dilution and within half an hour in the i in 6 

 dilution. 



These can be examined by drawing them up into a long pipette 

 separated bv an air bubble, or separate fluid drops on one large slide 

 or on separate slides. 



THE SPECIFIC GRAVITY OF THE BLOOD. 



From 1035 to 1068. 



To estimate it prepare a fluid of glycerine and water or chloroform 

 and benzol in known proportion about the normal specific gravity of 

 the blood. 



Place in it one drop of blood, and alter the specific gravity of the 

 .fluid bv adding glycerine and water or chloroform and benzol until 

 the drop neither floats nor sinks. The specific gravity of the fluid is 

 then that of the blood. 



THE SPECTROSCOPIC EXAMINATION. 



A small direct vision spectroscope is the most useful. 



Dilute the blood with distilled \\aler. 



Focus the spectrum, closing the slit as much as possible so as to 

 bring out Fraunhofer's lines distinctly. 



Oxy haemoglobin and reduced haemoglobin can be obtained from 

 the same specimen by shaking it up with air to oxidize it and adding 

 ammonium sulphide to reduce it. 



Oxyhiemogkjbin shows two narrow une([ual dark bands between 

 the lines D and E. 



