CHAPTER V. 45 



Objects should in all cases be removed from the fixing bath as 

 soon as 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. Alcoliol is almost always prefer- 

 able. Alcohol of about 70 per cent, may be taken, and (MAYER, 

 Intern. Monatsschr. Anat. Phys., 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. MAYER (Zeit. wiss. Mik., xiv, 1897, p. 28) 

 makes it by dissolving 5 grms. of iodide of potassium in 5 c.c. of distilled 

 water and mixing this with a solution of 0-5 grin, of iodine in 45 c.c. of 

 90 per cent, alcohol, but seldom uses the mixture concentrated, merely 

 adding as much, of it as is required to the alcohol or water containing 

 the objects. The important point is, that the iodine and iodide be 

 employed together. The iodine may be washed out in obstinate cases 

 with magnesia water. Similarly APATHY (Mitth. Zool. Stat. Neapel, xii, 

 1897, pp. 729, 730). 



It has been objected to this process that iodine in potassic iodide 

 precipitates corrosive sublimate instead of dissolving it. That is true, 

 but the precipitate is soluble in excess of the precipitant. 



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

 iodide may partly redissolve the precipitated compounds formed by the 

 sublimate with 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 alcohol, 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 in alcohol. 



It may happen that if the extraction of the excess of sublimate 

 from the tissues in bulk has been insufficient, crystals may form in 

 the sections after they have been mounted in balsam. This may 

 easily be prevented by treating the sections themselves with tincture 

 of iodine for a quarter of an hour before mounting. Some workers 

 hold that this does away with the necessity of treating the tissues in 

 bulk with iodine, which is frequently a very long process. Thus, 

 MANN (Zeit. wiss. Mik., xi, 1894, p. 479) prefers treating the sections 

 rather than the tissues in bulk, on the ground that the iodine makes 

 thenTsoft, so that they shrink on corning into paraffin. SCHAPER 



