342 SUMMARY OF CCTKUENT KESEAUCIIES RELATING TO 



polarization by reflexion should be complete, the tangent of the angle of 

 incidence, measured from the normal to the surface, should equal the 

 refractive index of the glass used. When this is 3/2, the angle is 

 56° 19'. (See letter 212, p. 188.) I see that Mr. Nelson uses 57°, which 

 is nearly the same. The selenite is not necessary, but adds much to the 

 beauty of the slides." 



B. Technique.* 

 CI) Collecting Objects, including' Culture Processes. 



Preparation of Culture-media containing Albuminous Fluids. f 

 P. Fildgs gives the following technique for the sterilization and prepara- 

 tion of albuminous culture-media : — 



Sterilization of Serum. — The serum should be collected at the 

 slaughter-house, horse serum being used on account of the rapidity with 

 which the corpuscles deposit. When horse serum is not available ox 

 serum may be used. The serum is collected as free as possible from 

 corpuscles and allowed to stand in the ice-chest in tall sterile jars about 

 2 in. in diameter. At the end of about five days the corpuscles will 

 be about half deposited. The separated serum is now distributed in 

 measured quantities (200 c.cm.) into perfectly fitting glass-stoppered 

 bottles, or into large glass bottles. Chloroform is added to each bottle 

 to make • 5 p.c. A drop of sterile oil is then applied to the stopper to 

 prevent sticking, and a dust-cover is fastened tightly over it. The 

 bottles are placed in the water bath at 45° C. for one hour, being shaken 

 occasionally. When they have cooled, a sample may be removed and 

 mixed with agar to test sterility (five days' test). When the serum is 

 required for any purpose entirely unaffected by heat, sterility may be 

 obtained by placing the bottles in the air incubator at 37° C, and 

 shaking occasionally. After twenty-four hours they will in most cases 

 be found to be sterile. When sterilized the serum is stored in a 

 cupboard. When required as a medium, the chloroform can be removed 

 by pipetting the serum off in measured quantities (50 c.cm.) into 

 200 c.cm. flasks, and then heating to 55° C. and placing under the 

 receiver of a pump. When a partial vacuum has been obtained, the 

 receiver containing the flasks is shaken and the chloroform then boils off. 

 The serum is now ready to incorporate in culture-media. 



Sterilization of Ascitic Fluid. — The ascitic fluid is collected from the 

 patient into a large glass bottle and allowed to stand in the ice chest for 

 a couple of days. The fluid is then decanted or filtered through glass 

 wool. The reaction is made slightly alkaline, or neutral with acid or 



* This subdivision contains (1) Collecting Objects, including Culture Pro- 

 oesses ; (2) Preparing Objects ; (3) Cutting, including Embedding and Microtomes ; 

 (4) Staining and Injecting ; (5) Mounting, including slides, preservative fluids, etc.; 

 (6) Miscellaneous. 



t The Lancet, cxcii. (1917) pp. 492-3. 



