28 FIXING AGENTS. 



formula somewhat coldly, pointing out (what was the case) 

 that Flemming recommended it merely for a very special 

 purpose, the hunting for karyokinetic figures, and that he did 

 not recommend it for general purposes. Further experience 

 has shown that ifc is applicable to general purposes, and will 

 probably be found for most purposes considerably superior 

 to the weak formula. I should use it by the hogshead if it 

 were not somewhat expensive.' 



Arnold, in the place quoted in the last paragraph, says that it is to be 

 avoided if you wish to demonstrate the structure of certain nuclei (of 

 wandering cells) ; and the other objections there quoted as applying to the 

 weak formula are intended to apply more or less to the present formula. It 

 will be well not to attach too much importance to them. Let delicate struc- 

 tures be fixed for twenty-four hours or more, washed in running water for 

 an hour, and in successive alcohols for twenty-four hours, sectioned, and 

 stained with safranin or gentian violet, and there will be little complaint of 

 defective preservation. 



The strong mixture does not brown tissues more than the 

 weak mixture, but rather less. 



Fat is blackened by these mixtures ; but the blackened fat can be entirely 

 dissolved out of the tissues by treating them for a few hours with turpentine 

 that has been exposed to sunlight for an hour or two (see Flemming in 

 Zeit.f. wiss. Mik., vi, 1, 1889, p. 39 ; and vi, 2, 1889. p. 178). 



PODWYSSOZKI recommends (for glands especially) the following modifi- 

 cation : 



1 per cent. Cro, 3 dissolved in 0'5 per cent, solution of cor- 

 rosive sublimate 15 c.c. 



2 per cent, osmium solution ...... 4 c.c. 



Glacial acetic acid 6 to 8 drops. 



This sublimate is said to augment the penetration of the osmium, but is 

 unfavorable to staining. The proportion of acetic acid is reduced in order 

 to avoid swelling of the tissue-elements (ZIEGLER'S Beitrage z. path. Anat.+ 

 i, 1886; cf. Zeit.f. wiss. Mik., iii, 3, 1886, p. 405). 



36a. Platino-aceto-osmic Acid (HERMANN'S solution). This 

 extremely important reagent is historically a modification of 

 Flemming' s solution, platinum-chloride being taken instead 

 of chromic acid. See next Chapter, 51. 



37. Nitric Acid (ALTMANN, Arch. Anat. u. Phys., 1881, p. 219). 



Altmann employs dilute nitric acid, containing from 3 to 3 per cent, pure 

 acid. Such a solution has a sp. gr. of about T02 ; an araeometer may con- 

 veniently be used to determine the concentration of the solution. Stronger 

 solutions have been used, but do not give such good final results. 



His (ibid., 1877, p. 115) recommended a 10 per cent, solution. Flemming 



