105 



cementing them to the slide, and the preliminary flooding to insure 

 their being free, was insufficient. In that case it is best to flood the 

 paper with clarifier, carefully lift it, arrange the sections again, flood 

 them with clarifier, place a clean piece of transfer paper over them 

 and try again. One soon becomes accustomed to the behavior of the 

 sections, and accidents are rare. In cutting a series of many small 

 sections, some time is consumed and it is necessary to flood the sec- 

 tions frequently with clarifier while cutting in order to prevent the 

 clarifier thickening and cementing them to the knife. 



60. Resume of the method. Success in the employment 

 of the collodion method depends upon the thorough infiltration with 

 the collodion solutions, requiring days or even months, and the em- 

 ployment of a thick imbedding mass giving when hardened a firm 

 unyielding support to the tissue. This may be gained by employ- 

 ing a relatively long period of infiltration, and taking pains in im- 

 bedding to have the collodion mass well thickened. 



Observing these two cautions, collodion may be used in almost 

 all cases as an imbedding mass, except such as are affected by the 

 conditions of the methods already mentioned ( 40 and 50) . 



THE FREEZING METHOD. 



6 1. This method is expeditious and of use in the rapid ex- 

 amination of tissues, and therefore especially serviceable in the 

 pathological laboratory and in clinical diagnoses. It may also be' 

 used in cutting tissues that are too hard to be cut satisfactorily by 

 means of either the collodion or paraffin methods. Both fresh and 

 fixed tissue may be cut by means of the freezing microtome and 

 with or without any special mass such as is used in paraffin or collo- 

 dion imbedding. 



When no mass is employed the tissue is simply frozen and cut, 

 or, if it is fixed tissue, soaked well in water first and then frozen. 

 When extreme haste is not so essential it is better to first saturate 

 the tissue with some solution that does not crystallize on freezing, 

 but simply hardens, since the formation of the ice crystals is hurtful 

 to the tissue. Such are solutions of gum arabic or sugar and anise- 

 seed oil, and they are spoken or as Congelation masses, 



62. Infiltration. Gum arabic or anise-seed oil may be 

 used, (a) Gum arabic. If the tissue has been fixed and is in alco- 



