GOLGI BODIES ETC. 319 



simple formalin fixation. Such fixation often gives delightful 

 results for such things as manuualian liver and brain, but poor 

 results for small invertebrates like crustaceans or worms. For 

 such animals Aoyama's fixative is the least bad, and we have had 

 some very fine results on Saccocirrus with Da Fano's fluid. On 

 the other hand, it is almost im])ossible to do any good with animals 

 like Daphnia or Cyclops. The finished sections are shrunken and 

 generally useless. There seems little doubt that the osmie 

 methods used, such as those of Nassonow and Weigl, are the 

 only reliable ones for most small invertebrates. 



Many Da Fano * and Cajal preparations we have seen have 

 been made carelessly, and the sections have been filled with 

 granular precipitates of silver. This makes the material unreliable 

 and useless for research ; such a fault is due to excess silver left 

 before the reduction stage. It has been concluded by a number of 

 workers that too long immersion in the fixative causes the mito- 

 chondria as ivell as the Golgi apparatus to become impregnated. It 

 is recommended to cut doxvn the fixation time as much as possible 

 and to make the pieces small. In such cases fixation will be complete 

 in one to tno hours. 



Results may be improved by fixing tissue in chilled Da Fano 

 or Cajal, and the worker is strongly recommended to try the cold 

 method as well as that at room temperature. 



720. The Supposed Chemical Basis of the Formalin Silver Nitrate 

 Techniques. A number of workers have noted that these methods 

 correspond somewhat to several techniques of doubtful specificity used 

 niicroeheniically to demonstrate chlorides. 



721. Golgi-Vehatti's Method (see Golgi, Aunt. Anz. Verh. Anat., 

 Ges., xiv, 1900, p. 174). Small pieces are hardened for a time varying 

 from a few hours to ten days or longer in Veratti's mixture, consisting 

 of— 



5 per cent, potassium bichromate . . 3 parts. 



01 per cent, chloroplatinic acid . . . 3 ,, 



1 per cent, osmic acid . . . . 3 ,, 



From time to time pieces are put in one or other of Golgi's rejuvenating 

 fluids (as descril)ed in §1035), and thence into 0-8 to 1 per cent, silver 

 nitrate. Sections are cut and mounted as by Golgi's bichromate and 

 nitrate of silver method (see § 1036). 



722. Golgi's Arsenious Acid and Silver Nitrate Method {Arch. Ital. 

 Biol., xlix, 1908, p. 272). Small pieces of quite fresh tissues are fixed 

 for three, six, eight or twelve hours in equal parts of 20 per cent, forma- 

 lin, saturated solution of arsenious acid, and 96 per cent, alcohol. After 

 a quick wash with distilled water, they are passed for some hours (or 

 days) into 1 per cent, silver nitrate, and then treated with a reducing 

 fluid, usually Cajafs hydroquinone mixture (hydroquinone 20 grm., 

 sodium sulphite 5 grm., formalin 50 e.c., water 1000 c.c.). Wash 

 quickly, dehydrate, and imbed either in eelloidin or paraffin. The 

 sections are toned with equal parts of 1 per cent, gold chloride and a 



* Da Fano preparations should be cleared in cedar wood oil, as xylol 

 shrinks them badly. 



