NEUROGLIA AND SENSE ORGANS 557 



cent, alcohol for twelve to twenty-four hours, washes them in 

 distilled water and then puts them into 1-5 per cent, silver 

 nitrate to which 10 per cent, pyridine has been added for twenty- 

 four to forty-eight hours at ST*^ C. After a rapid wash in distilled 

 water reduction is effected by a solution of 2 per cent, pyrogallic 

 acid, 90 c.c, pyridine 10 c.c, in ten to twelve hours. Frozen 

 sections may be cut or the material may be imbedded in paraffin. 



Braunmuiil {Zeitschr. f. d. ges. Neurol, u. Psychiat., cxxii, 

 1929, p. 317) uses frozen sections of well-fixed formalin material, 

 which after a thorough wash in distilled water are transferred to 

 20 per cent, silver nitrate for half an hour at 50 to 60° C. The 

 sections are washed in 1 per cent, ammonia and reduced in 20 per 

 cent, neutral formalin in tap-water for one to three seconds. The 

 washing in ammonia is repeated and the sections are then left in 

 formalin for five minutes, subsequently being well washed in 

 distilled water. They may be toned in gold chloride if desired. 



DiVRY {Riv. d. Pat. New., xl, 1932, p. 489) heats thin frozen 

 sections of formalin fixed material until vapour rises in Hortega's 

 solution for microglia 5 c.c, distilled water 5 c.c, pyridine 10 drops. 

 After a quick wash in distilled water the sections are reduced in 

 10 per cent, neutral formalin, washed well in distilled water, and 

 mounted in gelatin-glycerin. 



Although the above methods are more rapid, we have found 

 that Da Fano's modification of Bielschowsky's method for neuro- 

 fibrils is equally suitable for the demonstration of senile plaques. 



RETINA * 



1101. Fixation and Hardening. Notwithstanding the Encycl. 

 mik. Technik., 2nd ed., p. 75, we hold that osmic acid is by far the 

 best fixing agent. The retina of small eyes is best prepared by 

 fixing the entire unopened bulb with osmium vapours. 



Besides the sources quoted in the text, see Seligmann, Die mikro- 

 skopischen Untersiichungsmethoden des Auges, Berlin, S. Karger (Karl- 

 strasse 13), 1899 ; Greef, Anleitiing zur Mikr. Untersuch. d. Auges, 

 Berlin, Hirschwald, 3rd ed., 1910 ; the Art. " Retina " in Encycl. mik. 

 Technik., 2nd ed., p. 575 ; and D'Autrevaux, Technique Histo-bacterio- 

 logiqiie oculaire, Paris, 1926. 



Szent-Gyorgi {Zeit. f. iviss. Mikr., xxxi, 1914), uses the following 

 fluid :— 



Acetone . . . . . .125 c.c. 



Glacial acetic . 



Formalin 



Sublimate 



Aq. dest. 



Leave whole small eyes in 100 c.c. of this mixture for two to three 

 days, larger whole eyes six to seven days, after which one adds an addi- 

 tional 50 c.c. of acetone to the fixative and leaves for a further two or 



* A. B. L. and J. G .G. 



5 „ 



40 „ 

 4 grm. 

 100 c.c. 



