INFILTRATION OF TISSUE WITH CELLOIDIN AND PARAFFIN. 391 



others. The portion of the temporal bone containing the in- 

 ternal ear is especially resistant to these fluids. The following 

 fluids are the most useful : 



(a) Nitric Acid. Aqueous solutions should have a strength 

 of from 1 to 9 per cent. The time required varies considerably. 

 Foetal or very small bones are decalcified in a 1 per cent, solu- 

 tion in from three to ten days. For large pieces of adult 

 bone and for teeth, it is necessary to use a 3 to 9 per cent, 

 solution for many days. After decalcification the tissue should 

 be washed for twelve to twenty-four hours in running water. 



(b) Hydrochloric Acid. This is more generally useful than 

 nitric acid. It should be used in a 0.5 to 1 per cent, aqueous solu- 

 tion. In order to prevent a swelling of the tissues, normal salt 

 solution may be used instead of water. Ebner's hydrochloric- 

 acid-salt solution is made up of a cold saturated solution of salt 

 diluted with 2 volumes of water, together with from 2 to 5 per 

 cent, hydrochloric acid. This fluid acts slowly and should be 

 changed often. 



(c) Zenkers fluid is useful in decalcifying small pieces of 

 bone. It should be allowed to act for from two to three days. 



(d) A mixture of: chromic acid, 1 part; picric acid, 1 part; 

 glacial acetic acid, 5 parts: is a good decalcifying fluid for small 

 bones. 



(/) Infiltration of Tissue with Celloidin and Paraffin. 



In order to cut fixed and hardened objects into sections, it 

 is necessary to infiltrate them with a substance of even and 

 firm consistency. The substances commonly used are celloidin, 

 paraffin, and photoxylin. The tissue should be entirely de- 

 hydrated by means of absolute alcohol. For infiltration with 

 celloidin, this substance should be dissolved in a mixture of 

 equal parts of absolute alcohol and ether. This takes two or 

 three days, and a thick homogeneous fluid results. Three dif- 

 ferent thicknesses of this should be prepared in closely stoppered 

 jars. Photoxylin is dissolved similarly. It is more expen- 

 sive than celloidin, but has the advantage of being more trans- 

 parent. After being dehydrated in absolute alcohol, the 



