INTRODUCTION-. 13 



solution of oxalic acid ; these two portions are now to 

 be slowly mixed with constant stirring, and then 

 heated up to about the boiling point of water. 

 The solution is now filtered hot through flannel, 

 and is ready for use. An animal or organ injected 

 with this mixture should be kept warm during the 

 injection, as should all the utensils employed, so 

 that the gelatin may not harden prematurely and 

 stop the vessels. The injection may be made 

 with a syringe, or better with some form of appa- 

 ratus furnishing a constant pressure of variable 

 degree. 



IMBEDDING. 



It often occurs that a bit of tissue from which we 

 wish to prepare a section is too small or delicate to 

 be held in the fingers ; in such cases the object may 

 be placed between two bits of hardened tissue, such 

 as liver, tied around with a thread, and thus held 

 while the sections are made. Or, such a specimen 

 may be imbedded in a mixture of equal parts of 

 white wax and paraffin melted together, with ad- 

 dition of a sufficient quantity of olive oil to give 

 the mass the proper consistence for cutting when 

 cold. 



Certain tissues are very friable, so that thin sec- 

 tions fall apart as soon as they are made ; or they 

 may contain cavities so that they do not afford suf- 

 ficient resistance to the razor. In such cases the 



