CYTOLOGTOAL FIXING AGENTS. 329 



" 1. It does not give Millon's nor the xantho-proteic reactions. 2. It is easily 

 soluble in alkalies, soluble with difficulty in acids. 3. It is soluble in an 

 acetic acid solution of potassium ferrocyanide. 4. After treatment with 

 concentrated copper sulphate solution for twenty-four hours it loses its 

 affinity for stains. It is not, however, dissolved by the copper sulphate as 

 Schwartz stated. 5. It has a great affinity for anilin dyes, especially for 

 basic dyes like methyl green. If a mixture of methyl green and acid 

 f uchsin is employed, nucleic acid is stained green. The nucleins next richest 

 in phosphorus are stained a blue-violet tint, whereas the phosphorus-poorest 

 are coloured red. Now in the dividing nucleus, when the amount of chro- 

 rnatin is at its maximum, the nucleus stains green ; whereas in the resting 

 nucleus, where there is more pyrenin, a blue colour is observed." 



These considerations appear to justify the employment of the term 

 " chromatin " for the element of the nucleus that stains with methyl green, 

 the term " nuclein " having obtained a wider extension. 



See also KOSSEL, in BEHRENS, KOSSEL, und SCHIEFFERDECKER'S Das 

 Mikroskop, &c., ii, p. 47 ; the same, in Verh. d. physiol. Ges., Berlin, Oct. 

 21st, 1892 ; and MALFATTI, Ser. d. naturw. med. Vereines in Innsbruck, 

 1891-2. 



For the microchemical detection of phosphorus in tissue-elements see the 

 paper of LILIENFELD and MONTI, in Zeit. f. physiol. Chemie, xvii, 1892, 

 p. 410 (Report in Zeit.f. wiss. Mik., ix, 3, 1893, p. 332) ; also a short notice 

 in HALLIBTJRTON'S Goulstonian Lectures, 1893 (see Brit. Med. Journ., 

 March llth, 1893, p. 505). 



637. Cytological Fixing Agents. The following is in great 

 part taken from the numerous papers of FLEMMING in the 

 Arch. f. mik. Anat. from the year 1879 onwards, and from his 

 Zellsubstanz, Kern- und Zelltheilung. 



Osmic acid (y 1 ^- to 2 per cent.) preserves the form of the 

 entire cell, but swells the nuclei and rounds off nucleoli. It 

 renders the nuclear "reticulum" undiscernible. Picric acid, 

 either concentrated or dilute, and chromic acid, O'l to 0*5 per 

 cent., are to be preferred to alcohol and other agents for the 

 study of the cells of Vertebrates. Shrinking and distortion of 

 the nuclear figures (and, with picric acid, swellings of them) 

 are to be expected, but other agents have the same defect to 

 a much greater degree ; alcohol especially causes entanglement 

 of the filaments. Acetic acid does the same, and causes 

 swelling besides. Stronger chromic acid solutions cause 

 shrinking. Neither of these reagents is harmless as regards 

 the nuclei of red blood-corpuscles. The salts of picric acid 

 (potash-, soda-, and baryta-salts) are most harmful. Weak 

 (i. e. not more than 1 per cent.) acetic, hydrochloric, or nitric 

 acid, combined with clearing in glycerin and staining, may be 



