APPENDIX. 



The important processes of interstitial embedding are two, paraffin 

 and celloidin being the substances respectively used to infiltrate the 

 tissue ; of these the paraffin method must be regarded as the most 

 perfect, and, with few exceptions, to be preferred whenever thin per- 

 fect sections are of importance, especially where preservation of 

 sequence is desirable. 



Paraffin Method {Klebs). 



The essential point of this process is thorough and complete im- 

 pregnation of the tissue with the embedding mass ; it is conse- 

 quently necessary to saturate the tissue with some fluid with which 

 the paraffin is perfectly miscible, the fluids usually employed to this 

 end being chloroform or turpentine oil ; in order, however, to insure 

 the free entrance of these fluids within the tissue, it is first necessary 

 to free the tissue of all traces of water still contained in the alcohols 

 of 70 or 80 per cent. It is, therefore, necessary to place the tissue 

 from the usual 80 per cent, preserving spirit as follows : * 



a. Into 95 per cent, alcohol horn 12 to 24 hours. 



b. Into absolute alcohol from 24 to 48 hours, until complete dehy- 

 dration has been secured ; this step is of the utmost importance for 

 the success of all the subsequent manipulations, since if dehydration 

 be imperfect infiltration will be unsuccessful, and the tissue will cut 

 badly. 



c. Into pure chloroform from 6 to 8 hours, or until the chloroform 

 has replaced the absolute alcohol ; an indication of the completion 

 of this interchange is furnished by the position of the tissue, since as 

 soon as the tissue continues to lie beneath the surface of the chloro- 

 form, or sinks towards the bottom of the bottle, it may be concluded 

 that the alcohol has been completely replaced by the chloroform. 



d. Into a saturated solution of paraffin in chloroform from 2 to 3 

 hours ; the solution may be kept slightly warmed. 



e. Into pure melted paraffin, which has a melting-point of about 

 50 C. ; the paraffin is best contained in a small open porcelain cap- 

 sule placed within a water-oven so regulated as to maintain a constant 

 temperature of about 50 C. ; while undesirable, congealment of the 

 surface of the paraffin due to reduction in temperature is no great 

 misfortune, the retarded evaporation of the chloroform being the 

 principal evil ; a rise of the temperature to which the tissue is sub- 

 jected to a point beyond 55 C. , on the contrary, is usually disastrous, 

 the tissue being shrunken and distorted to a degree which renders it 

 valueless. It is, therefore, desirable to keep the paraffin and the 



* In the appended data it is still assumed that the tissue being treated is of the 

 consistence and volume represented by a piece of kidney 2 cubic cm. in size. 



