46 CHAPTER V. 



solution obtainable. For some very contractile forms (coral 

 polypes, Planaria), a concentrated, solution in warm or even 

 boiling water should be employed. For Arthropoda alcoholic 

 solutions are frequently indicated. Delicate objects, however, 

 may require treatment with weak solutions. 



Objects should in all cases be removed from the fixing 

 bath as soon a.s' fixed, that is, as soon as they are seen to have 

 become opaque throughout, which may be in a few minutes 

 or even seconds. 



Wash out with water or alcohol. Alcohol is almost always 

 preferable. Alcohol of about 70 per cent, may be taken, 

 and (Mayee, Intern. Monatsschr. Anat. Fhyn., iv, 1887, p. 43) 

 a little tincture of iodine may be added to the liquid, either 

 alcohol or water, used for washing, enough to make it of a 

 good port-wine colour, and the mixture be changed until it 

 no longer becomes discoloured by the objects. Apathy 

 {Mikrotechnik, p. 148) takes a 0'5 per cent, solution of iodine 

 in strong alcohol, leaves the objects in it (suspended) until 

 they have become of about the colour of the solution, and 

 then washes for twenty-four hours in pure alcohol. 



In obstinate cases solution of iodine in iodide of potassium (e.g. 

 Lugol's) may be taken. Mayee {Zeit. wiss. Mik., xiv, 1897, p. 28) makes 

 it by dissolving 5 grammes of iodide of potassium in 5 c.c. of distilled 

 ■water and mixing tbis with a solution of 0'5 gramme of iodine in 45 c.c. of 

 90 per cent, alcobol, but seldom uses tbe mixture concentrated, merely 

 adding as muob of it as is required to tbe alcobol or water containing 

 tbe objects. The important point is, tbat tbe iodine and iodide be em- 

 ployed together. Tbe iodine may be wasbed out in obstinate cases witb 

 magnesia water. Similarly Apathy (Mitth. Zool. Stat. Neapel, xii, 

 1897, pp. 729, 730). 



It bas been objected to tbis process tbat iodine in potassic iodide pre- 

 cipitates corrosive sublimate instead of dissolving it. Tbat is true, but 

 tbe precipitate is soluble in excess of tbe precipitant. 



Tbe iodide of potassium process should be employed with care, for the 

 iodide may partly redissolve tbe px-ecipitated compounds formed by the 

 sublimate witb the albuminoids, etc., of the tissues, and it may be well 

 not to begin adding the iodine till the objects have been brought into 

 fairly strong alcobol, 70 or 80 per cent. 



It is important that the sublimate be thoroughly removed 

 from the tissues, otherwise they become brittle, and will not 

 stain so well. They will also become brittle if they are kept 

 long ill alcohol. 



