.496 PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS 



of these, it is the paraffin method that is by far the most usually 

 employed. It is the most convenient for ordinary work, the 

 collodion method only presenting points of superiority in special 

 cases, such as the sectioning of extremely large objects, or very 

 brittle tissues, and other special circumstances. 



The Paraffin Method. The first step in the paraffin method 

 consists in saturating the objects with a solvent of paraffin. The 

 second consists in saturating them with molten paraffin, which 

 gradually takes the place of the solvent. The third consists .in 

 causing the paraffin to solidify, and arranging the solidified mass in 

 ti suitable form for cutting sections. The fourth consists in cutting 

 the sections and freeing them from the solid paraffin with which 

 they are saturated, and if desired affixing them in serial order to a 

 slide for the purpose of mounting. 



1. Saturation ivith a solvent. The solvents employed are either 

 chloroform, or one of the volatile hydrocarbons, such as benzol, 

 toluol, or naphtha, or an essential oil, such as oil of cedar or oil of 

 cloves. None of these are miscible with water, but all of them are 

 miscible with alcohol. Therefore the objects to be imbedded are in 

 the first place thoroughly dehydrated with alcohol, according to the 

 principles set forth above, p. 487. The alcohol is then removed 

 from the objects, and the solvent is made to take its place gradually 

 by one of the substitution methods described above, p. 487, under 

 * Clearing.' Cedar oil is one of the most convenient solvents ; and 

 .as it is at the same time one of the best of clearing agents, it follows 

 that any object that has been cleared in it is at once ready for 

 saturation with paraffin. Other essential oils, such as clove oil, may 

 .also be employed. But the two best saturation agents are certainly 

 oil of cedar and chloroform. It will be noticed that the best way to 

 saturate objects with chloroform is to place the chloroform under 

 the alcohol, and allow the substitution of liquids to take place just 

 as in clearing with a non-volatile clearing agent, as directed 

 above, under ' Clearing.' 



2. Saturation with paraffin. If cedar oil, or other non-volatile 

 medium, has been employed, proceed as follows : Melt some 

 paraffin in a suitable vessel a watch-glass will do for small objects 

 and keep it as nearly as possible at melting-point on a water-bath 

 or in a stove, taking care to keep it protected from vapour of water. 

 Remove the object from the oil, and put it into the paraffin, and 

 leave it there till thoroughly saturated. The length of time 

 required for this must be found by experience. A piece of 

 soft tissue of J inch thickness is generally well saturated in an 

 hour. If the objects be at all large, the paraffin should be 

 changed for fresh once or twice, so that none of the oil may remain 

 "to contaminate it and render it soft after cooling. 



Some persons prefer to bring the objects gradually from the oil 

 into the paraffin by passing them through graduated mixtures of oil 

 -and paraffin ; but with cedar oil, at all events, that is not necessary. 



If chloroform, or other volatile medium, has been employed, 

 the procedure may be modified in the following manner, which is 

 very advantageous for delicate objects : 



