CH. VII.] COLLODION SECTIONING. 157 



THE PREPARATION OF SECTIONS OF TISSUES AND ORGANS. 



£ 250. At the present time there are three principal methods of ob- 

 taining thin sections of tissues and organs for microscopic study. These 

 methods are : The Collodion Method, the Paraffin Method, and the Freez- 

 ing Method. Each of these methods has its special application, although 

 the collodion method is perhaps the most generally applicable, and the 

 freezing method the most restricted, and is used mostly in pathological 

 work, where rapid diagnosis is necessary and the finest details of struct- 

 ure are not so important. With the paraffin method the thinnest sec- 

 tions may be made, and in some ways it is the most satisfactory of all. 

 A good microtome is of very great aid in sectioning. 



§251. The Collodion Method. — In sectioning by this method the 

 tissues are first hardened properly and then entirely infiltrated with col- 

 lodion, and the collodion hardened. It is not removed from the tissue, 

 but on account of its transparency does no harm. 



£ 252. Fixing and Hardening the Tissue. — Any of the approved 

 methods of hardening and fixing may be employed. A good general 

 method which is applicable to nearly all of the tissues and organs is that 

 by Picric- Alcohol. For the preparation of the solution see (§ 315). A 

 small piece of tissue or organ not containing more than two to three 

 cubic centimeters is placed in 40 or 50 cc. of the picric-alcohol and left 

 6 to 24 hours, when the first picric-alcohol should be thrown away and 

 fresh added. After one or two days more the picric-alcohol should be 

 poured off and 67'/ alcohol added. In a day or two this is replaced by 

 75 c /c or 82 r /c alcohol ; 82'/ is on the whole most satisfactory, and the 

 tissue may be left in this till it is ready for dehydration. 



§ 253. Dehydration before Infiltration. — When one is ready to 

 imbed for sections, the tissue must first be dehydrated in plentiful 95$ 

 or stronger alcohol. It is better to take only a small piece for this. 

 The smaller the piece the thinner the sections may be made. The de- 

 hydration will usually be completed in 2 to 24 hours. If the alcohol is 

 changed two or three times the dehydration will be hastened. 



§ 254. Saturating with Ether- Alcohol (§ 306). — The next step is 

 to remove the tissue from the alcohol and place it in a vial of ether- 

 alcohol (§ 306) for 2 to 24 hours. The dehydration is somewhat more 

 complete by this step, and the tissue is more perfectly prepared for the 

 reception of the collodion. If the dehydration is very thorough in the 

 alcohol, this step may be omitted, however, but one is surer of success 

 if the ether-alcohol is used. 



§255. Infiltration with Thin Collodion. — The ether - alcohol is 

 poured off, and a mixture of thin collodion is added (§ 304). Two or 



