CUTTING OF SECTIONS. 536 



ing 1 part of gelatin, 2 parts of water and 4 parts of gly- 

 cerin. The cork is then securely clamped to the microtome 

 and the sections are cut. The tissue and knife must be kept 

 moistened with alcohol and the sections are transferred at 

 once to alcohol by means of a camel-hair brush. 



Frozen sections.- — The tissue fixed and hardened in alco- 

 hol may be cut by means of the freezing microtome. It 

 should not be more than 2 or 3 mm. thick. The alcohol 

 must first be removed from the hardened tissue by immer- 

 sion in water. This can be accomplished in cold water in 

 from 4 to 8 hours, depending on the size of the piece. If the 

 water is warmed to 38° the alcohol will be removed more 

 rapidly, in from 1 to 2 hours. The tissue can then be frozen 

 by the ether spray apparatus and sections cut. The knife 

 is moistened with water and each section is at once trans- 

 ferred to water. This method is very useful in the staining 

 of bacteria in tissues. 



Paraffin sections. — The paraffin block is trimmed square 

 and then firmly attached to the metal holder. When cut- 

 ting paraffin sections the knife must be kept perfectly dry. 

 Moreover, the edge of the knife should be parallel to that 

 of the block. In other word^, the knife is not fixed in a 

 slanting position as in the case of alcohol hardened or cel- 

 loidin imbedded objects. 



This method of imbedding and cutting sections is easy 

 of execution and thinner sections can be obtained than by 

 any other procedure. It is to be preferred to the others 

 for making bacteriological examinations of tissue. The 

 paraffin sections are transferred from the knife by means of 

 a brush or needle to a piece of clean filter-paper, which is 

 covered by a bell- jar. Before staining the sections it is, as 

 a rule, necessary to remove the paraffin. This can be 

 readily done by means of toluol, xylol or turpentine. The 

 sections, contained in an Esmarch dish, should be washed 



