362 



METHODS. 



rapidity. It is adapted only for paraffin work. For the general use of students, 

 in elementary courses especially, this microtome is to be preferred to the " preci- 

 sion," as it requires less care and works more rapidly. A single rotary micro- 

 tome will be found sufficient for a class of from twenty to thirty students in 

 embryology. 



The microtome is an instrument of precision, which implies that it must be 

 treated with extreme delicacy and kept most scrupulously clean. It will be 

 found usually, when complaint is made against the microtome, that the com- 

 plaint is misdirected, and ought to be not against the machine, but against the 



FIG. 218. THE AUTOMATIC ROTARY MICROTOME. 



owner. The modern microtome necessarily has several adjustments, every one 

 of which must be exact and secure. If any one of them is imperfect and insecure, 

 if any of the movable parts are allowed to become corroded, or gummed up with 

 oil, or loose, or clogged with dust or dirt of any kind, the microtome will not and 

 cannot work as an instrument of precision. The knife used for cutting ought to 

 be regarded as an integral part of the microtome and as its most delicate and 

 easily injured part. A perfect knife-edge is the greatest treasure of the micro- 

 tomist. To sharpen the knife satisfactorily for fine section cutting is a really 

 serious difficulty. A skilful person, however, may get a good edge by using the 



