FIXATION OF TISSUES. 389 



very irritating to the mucous membranes, and the eyes should 

 be protected in using it. Osmic acid forms a part of many 

 fixing mixtures. Tissues fixed thus should be washed for 

 from twenty-four to forty-eight hours in running water. 



(3) Flemming's fluid (chrom-osruium-acetic acid) has the 

 following constitution : 1 per cent, chromic acid, 15 parts ; 

 2 per cent, osmic acid, 4 parts; glacial acetic acid, 1 part. The 

 tissue is left in this from three hours to three days, and then 

 washed one day in running water. 



(4) Hermann's fluid (platinum-osmium-acetic acid) consists 

 of 15 cc. of 1 per cent, aqueous platinum chloride solution ; 

 4 cc. of 2 per cent, osmic acid ; 1 cc. of glacial acetic acid. 

 This is used in the same way as Flemming's fluid. It has the 

 disadvantage of being expensive. 



The last three fluids can be used in relatively small 

 quantities. 



(5) Midler's fluid consists of 2-2 grammes of potassium 

 bichromate, 1 gramme of sodium sulphate, and 100 cc. of 

 water. A large quantity of this fluid should be used. It 

 should be kept in the dark when used, and the tissues are left 

 in it, according to their size, for from six weeks to three 

 months. In the first weeks the fluid should be changed every 

 day or two, and after that twice a week. Miiller's fluid is 

 especially useful in fixing the central nervous system. Fairly 

 large pieces of tissue can be used. 



(6) Erlicki's fluid consists of 2i grammes of potassium 

 bichromate, 1 gramme of copper sulphate, and 100 cc. of 

 water. It resembles Miiller's fluid in its action, but fixes 

 the tissue in one-third of the time. 



(7) Corrosive sublimate (bichloride of mercury) acts best as 

 a warm saturated solution in physiological salt solution, with 

 the addition of 1-5 cc. of glacial acetic acid to 100 cc. of the 

 fluid. The duration of its action varies according to the size 

 and density of the tissue, for from one to twenty-four hours. 

 With fluids containing corrosive sublimate, no metal instruments 

 should be used. Tissues so fixed should be washed carefully in 

 running water for from twenty-four to forty-eight hours. 



