Febkuary 8, 1895.] 



SCIENCE. 



167 



sue is transferred to the silver nitrate solu- 

 tion {\%). Or the tissue after 1 to 2 days 

 may be transferred from the above bichro- 

 mate-formalin mixture to the following : 

 Pot. bieh. (5/f ) '2 vols. + formalin 1 vol. 

 After 12 to 24 hours the tissue is put into 

 silver solution. The advantages of this 

 method are that it avoids the use of osmic 

 acid and that the stage of hardening 

 favorable for impregnation lasts longer than 

 when the osmium-bichromate mixture is 

 used and good results are consequently 

 more certain. lu other words, the forma- 

 lin-bichromate does not overharden. In 

 this respect it is also superior to the lithium 

 l)ichromate method of the author (N. Y. 

 Acad, of Sc. Pro. vol. XIII., 1S94). For 

 embryonic tissue the formalin method is 

 probably not equal to the osmium-bichro- 

 mate method, possibly because it does not 

 liardeu sufficiently. For such tissue lHh- 

 inm bichromate (which hardens more 

 rapidly tlian potassium bichromate) had 

 better be mixed with the formalin instead 

 of potassium bichromate. While good results 

 are obtainable, especially with advanced 

 embryonic tissue, with either of the above, 

 yet the author belitives that for such tissue 

 the osmium-ljicliromate method is prol)ably 

 in certain respects somewhat superior. 



A fuller account will be published later. 



Dr. Ira Van Gieson reported some pre- 

 liminary observations on the action of for- 

 malin as a fixative and preservative of the 

 central nervous system for the ordinarj' his- 

 tological staining methods ; solutions of Ibr- 

 malin, four, six and ten per cent, were used, 

 followed bj- 9.^ per cent, alcohol and celloi- 

 din embedding. Sections of the human cord, 

 cerebellum and cortex prepared in this way 

 gave very thorough fixation of the ganglion 

 cell, neuroglia cells, and fine nerve fibres. 



Weigert's haematoxylin method can be 

 applied to such sections, and gives very 

 good results for the plexus of fine fil)res in 

 the cortical and spinal grey matter. The 



mjelin of the fine fibres is well preserved 

 and gives the characteristic bluish black re- 

 action with the "Weigert liaematoxylin stain, 

 as in chronu> hardened preparations. The 

 background of the grey matter is especially 

 clear and the fibres sharply delineated. 

 The formalin hai-dened sections should be 

 soaked in the neutral copper acetate solu- 

 tion, diluted one-lialf \nth water, for 2 

 hours, then thoroughly washed in water and 

 immersed in the Weigert lithium-carljonate 

 haematoxylin solution two to twelve hours. 

 Weigert's borax-prussiate of potassium so- 

 lution is used for differentiation. The dif- 

 ferentiation takes place rapidly and must be 

 watched carefullj-. 



The formalin sections of the central 

 nervous sj'stem maj- also be used for Rehm's 

 modification of Nissl's method ; but the 

 staining of the chromatin and minute struc- 

 ture of the nucleus and cj-toplasm is not 

 quite so shai-plj' outlined as with absolute 

 alcohol fixation. 



The duration of the hardening in formalin 

 solutions has a verj- important and \ arying 

 influence on the nerve fibers and ganglion 

 cells with reference to the application of 

 such methods as the Weigert and Nissl 

 groups of stains. A further study to define 

 the more exact limitations of formalin as a 

 new histological pres^■l'^•ative for the nervous 

 system will be published later and the more 

 exact periods of time in the hardening ne- 

 ces.sary lor different stains detailed. 



Mr. R. H. Cunningham, On the Souvvea of 

 Illumination for Phufo-Micrographi/, noted a 

 practical mode of employing the arc light 

 with satisfactory results. 



Mr. C. F. Cox ilhistrated the Latest Theories 

 of Diatom Stntetiire, exliibiting lantern slides 

 of Mr. T. F. Smith, of London. 



Dr. Edward Learning projected a series 

 of his micro-photographs of bacteria, fer- 

 tilization processes of sea-urchin, Toxo- 

 penemtes, and Golgi preparations. 



Bashford Dean, Recording Secy. 



