400 SUMMARY OF CURRENT RESEARCHES RELATING TO 



obtained excellent results by the following method, which renders the fine 

 medullated nerve-fibres coursing in the grey matter very distinct and 

 conspicuous. A piece of fresh tissue from cortex or cord, not exceeding 

 1/8 in. in thickness, is placed in a mixture of 2 per cent, osmic acid 

 8 ccm. and 1 per cent, acetic acid 2 ccm. If the mixture be darkened 

 within 24 hours, it should be renewed. After 48 hours the piece is 

 immersed in 10 per cent, formalin for three days, and is then imbedded 

 in paraffin or celloidin. The sections are passed through 1 • 5 per cent, 

 permanganate of potash solution and 1 per cent, oxalic acid solution until 

 differentiation is complete. They are then treated in the usual manner. 



The modification of Marchi's method consists in immersing pieces 

 of central nervous tissue which have been hardened in bichromate, in 

 the aceto-osmic acid solution just described for ten days. This addition 

 so increases the penetrating power of osmic acid, that the central portions 

 of the block are found to give the Marchi reaction quite as well as the 

 peripheral. 



The author has found that the initial stages of fixation and harden- 

 ing may be hastened by using a mixture of 2 per cent, bichromate and 

 5 per cent, formalin for 24 hours, and then removing to 2 per cent, 

 bichromate. 



Modification of Marchi's Method of Staining Degenerated Nerve- 

 fibres.* — Mr. J. N. Langley and Mr. H. K. Anderson adopt the follow- 

 ing procedure for preventing nervous tissue from becoming brittle, and 

 for enabling adjoining sections to be stained by other methods. After 

 hardening in 2 per cent, potassium bichromate or in Miiller's fluid, the 

 pieces are placed for a day in a solution of gum in 2 per cent, potassium 

 bichromate. Sections made with a freezing microtome are removed to a 

 2 per cent, potassium bichromate solution to wash out the gum. Suc- 

 cessive sections may then be placed in : — (1) a mixture of potassium 

 bichromate and osmic acid to stain the medulla of the degenerated fibres, 

 and may be left therein for 1-3 weeks ; (2) in water, then in alcohols 

 up to 70 per cent, to remove the fixative and to harden somewhat ; then 

 back through alcohols to picrocarmine or other stains ; (3) chrome-alum 

 mixture, and stained by the Weigert-Pal method as modified by Heller 

 and by Ford Eobertson. 



The writers find that spinal cord may be kept for more than a year 

 in potassium bichromate, and still give the Marchi reaction by the fore- 

 going method. 



Staining Gonococci in Living Leucocytes.! — Herr Plato mixed a 

 droplet of pus with a loopful of neutral red solution (1 ccm. of cold 

 saturated aqueous neutralised solution and 100 ccm. of physiological salt 

 solution), and on examining as a hanging drop found that the intra- 

 cellular gonococci were stained deep red. Warming the stage excited 

 amoeboid movements, and during this phase the cocci lost their colour, 

 regaining it when the movements ceased and the granular condition of 

 the leucocyte was resumed. It is stated that intracellular gonococci 

 have a greater receptivity for the pigment than other organisms, while 



* Proc. Physiol. Soc, p. xxxi. See Journ. of Physiol., xxiv. (1899). 

 t Berlin Klin. Wochenschr., 1899, No. 49. See Centralbl. Bakt. u. Par., l u Abt., 

 xxvii. (1900) pp. 286-7. 



