Apr] cutting sections. 251 



In any case the cutting-blade should for the 

 first method of imbedding be kept freely wetted 

 with spirit; and each section, as it is made, carefully 

 floated on to a glass slide and then, the spirit 

 having been removed, mounted in glycerine, or 

 treated with creosote or oil of cloves and turpentine 

 and mounted in balsam or dammar. It is well to 

 guard the section with a small diaphragm of paper 

 placed under the cover-slip. 



When the object has been imbedded in sper- 

 maceti in the way recommended above, the block 

 of spermaceti and the razor should be moistened 

 with olive oil and not with spirit. The sections 

 must be floated from the razor on to the glass 

 slip in the ordinary way and then treated with a 

 mixture of turpentine (4 parts) and creosote (1 

 part) till all the oil and the spermaceti are removed. 

 They may then be mounted in Canada balsam or 

 dammar in the usual way. Even when the other 

 methods of imbedding spoken of above are adopted, 

 it will frequently be found advantageous to moisten 

 the razor with creosote or oil of cloves rather than 

 with spirit. 



Whichever method be followed, a series of sec- 

 tions, each as thin as possible, should be obtained 

 and carefully numbered, from head to tail or vice 

 versa. They should at first at least all be retained 

 for study, and not even the fragmentary ones 

 thrown aw^ay, these being often the most instructive. 



The following transverse sections will perhaps 

 be the most instructive. 



1 . Through the optic vesicles, shewing the optic stalks. 



2. Through the hind-brain, shewing the auditory sacs. 



3. Through the middle of the heart, shewing its rela- 

 tions to the splanchnopleure and alimentary canal. 



4. Through the point of divergence of the splanchno- 

 pleure folds, shewing the venous roots of the heart. 



5. Through the dorsal region, shewing the medullary 



