ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 297 



hours, that is to say, pure cultivations could be obtained by transference 

 to gelatin. After about six hours the colonies were no longer pure. 



Solid Media prepared from Milk.* — Dr. Van Puteren produces 

 solid media for the cultivation of micro-organisms from milk in the 

 following manner. The milk is evaporated with rennet which contains 

 no pepsin, and it is then filtered in a vacuum. This procedure will 

 produce a sufficiently transparent medium in 3/4 to 1 hour, and if 

 gelatin or agar be added, in 1^ to 2 hours a crystal clear medium is 

 obtained. The milk whey is prepared as follows. 1 litre of skim milk 

 is poured into a tin saucepan holding 1^ litre ; to this is added 5-6 ccm. 

 of rennet essence, and the mixture warmed over a Bunsen's burner to 

 40°-42°. When coagulation has set in (3-5 minutes) the mixture is 

 filtered through gauze folded eight times. The filtrate, amounting to 

 860-880 ccm., is repoured into the saucepan, and 6 to 10 per cent, dry 

 gelatin and the albumen of two eggs added. When dissolved the fluid 

 is again filtered, and 2 per cent, of sodium albuminate is added. It is 

 then neutralized with a weak solution of caustic potash, and afterwards 

 filtered through a simple cotton-wool filter moistened with hot water in 

 an exhausted space. 100 ccm. of distilled water are afterwards added 

 to make up for the loss in boiling. The filtrate sets well, and is suit- 

 able for all bacteriological work. If a crystal clear solution be desired 

 the filtration as before must be repeated, and afterwards through a paper 

 filter on a Plantamour's hot funnel. 



Another solid medium is made with agar. The same procedure is 

 adopted, the only differences being that 1 per cent, of agar is added to 

 the filtrate and 1 per cent, of sodium albuminate. 



A list of some thirty micro-organisms examined on these media is 

 given. The list includes Blastomycetes, Hyphomycetes, and Schizo- 

 mycetes. 



C2) Preparing: Objects. 



Demonstrating Transverse Striations in Axis-cylinders and Nerve- 

 cells."!" — M. J. Jakimovitch, who has been examining by the silver 

 method the transverse striations on the axis-cylinders of the central and 

 peripheral fibres, has found that similar striations exist in the large 

 nerve-cells of the anterior cornua. The following method is recom- 

 mended : — 



Very small pieces of nerve or spinal cord from a recently killed and 

 healthy animal are placed in silver solution in the dark. I'or the cen- 

 tral nerves the solution should be 1/4 per cent., for the peripheral 1/2 

 per cent., and for the nerve-cells 1 per cent. The nerves are left 

 24 hours, the cells 48 hours in the solution. The preparations are then 

 carefully washed in water and exposed in this to the light. When the 

 preparation has become of a dark brown colour it is placed in a mixture 

 of formic acid (1 part), amyl-alcohol (1 part), and water (100 parts). 

 The object exposed to the light in this mixture for 2 or 3 days at first 

 becomes brighter, a part of the reduced silver being dissolved ; hence 

 the mixture must be renewed from time to time. When all the silver 

 has dissolved a darker colour is permanently assumed. The nerve-cells 

 are left in this mixture for 5 to 7 days. 



* Wratsch (Russian), 1888, No. 15. Cf. Centralbl. f. Bacteriol. u. Parasitenk., 

 V. (1889) p. 181. 



t Jouin. de I'Anat. et de la Phvsiol., xxiii. (1888) pp. 142-67 (1 pi.). 

 1889. ' X 



