38 FIXING AND HARDENING AGENTS. 



HENNEGUY, who has worked a great deal with this reagent, and 

 recommends it highly, says (Lecons sur la Cellule, p. 61) that it is 

 well only to add the acetic or formic acid just before using, as it 

 frequently reduces the osmium and platinum very rapidly and 

 energetically. He finds that it contracts the more spongy sorts of 

 protoplasm less than mixture of FLEMMING. I think highly of it 

 for certain objects. Twelve hours is probably the optimum time 

 for fixation. Wash out in water. 



45. Platino-aceto-osmic Acid (HERMANN'S) Solution (Arch. Mik. 

 Anat., xxxiv, 1889, p. 58). One per cent, platinum chloride 15 parts, 

 glacial acetic acid 1 part, and 2 per cent, osmic acid either 4 parts 

 or only 2 parts. Hermann found that protoplasm structures are 

 thus better preserved than with the chromic mixture. As with 

 Flemming, the optimum time is from twelve to sixteen hours. 

 Wash out at least three hours in running water. 



The after-treatment and staining should be the same as for objects 

 treated with Flemming's solution. RENGEL (Zeil. wiss. Zool., 

 Ixiii, 1898, p. 454) washes out for half an hour to an hour with 

 saturated aqueous sol. of picric acid, which he thinks facilitates the 

 staining, especially of nuclei. 



The action of this fixative is, roughly, similar to that of Flemming's. 

 Like Flemming's, it mordants chromatin for staining with " basic " 

 colours, with which it affords equally fine nuclear stains. But, 

 owing to the platinum in it, it diminishes more than Flemming's the 

 colorability of tissues with " acid " colours, so that- it is extremely 

 difficult to obtain good plasma stains after its action. It causes a 

 notable shrinkage in chromatin. It gives a full fixation of cyto- 

 plasm,, to which it gives a much more fine-grained aspect than liquid 

 of Flemming does. 



Leaving out the acetic acid, the solution may be used for mito- 

 chondria as in 679. 



46. Rawitz (Zeit. wiss. Mikr., xxv, 1909, p. 386) takes 4 parts of 

 Kahlbaum's Phospho-Tungstic acid, 5 of alcohol, and 1 of acetic acid, 

 added just before use, fixes for twenty-four hours, and washes out 

 the sections before staining with water containing a little calcium 

 acetate. 



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

 Altmann employs for fixing embryos dilute nitric acid, containing from 

 3 to 3 per cent, pure acid. Such a solution has a sp. gr. of about 1-02. 

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

 results. After extensive trial I find ALTMANN'S solution to be a second- 

 rate reagent, giving a weak and thin fixation. 



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



