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* 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 (MAYER, Intern. Monatssclir. Anat. Phy*., 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 

 (Mikrotechnilt, 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 grammes of iodide of potassium in 5 c.c. of distilled 

 water and mixing this with a solution of 0'5 gramme 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 em- 

 ployed 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 pre- 

 cipitates 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 1 ,., 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. 



