CH. X] 



FIXATION OF TISSUES 



285 



parts of the body quickly, and that is done by washing out the vascular sys- 

 tem with normal salt solution and then filling the vascular system with the 

 fixer. This method of "fixation by injection " is of great importance in the 

 histology of animals which are large enough to inject. 



If the animal is too small for injection or one wishes only a small part of 

 a larger animal, then the pieces for fixation should be small, say one to three 

 cubic centimeters. Often as for Flemming's fluid (§ 405) and for several 

 others it is better to use pieces 2 to 5 cubic millimeters. 



Large, solid organs, must be cut into several pieces if the whole is needed. 

 For hollow organs the cavity ma3' be filled with the fixer and the organ placed 

 in a vessel of the same. 



Figs. 223-224. Shell vial and a Comstock bent-neck vial for fixing and 

 storing material for histology. The Comstock bent-neck vial is especially 

 designed for elongated objects like fish embryos, insects, etc., which are liable 

 to become bent in a vertical bottle. (Cut of the bent-neck, from the Whita.ll 

 Tatum Co.) 



The amount of fixer should be 10 to 50 times that of the piece of tissue. 



Of the fixers given under "Preparation of Reagents," Picric alcohol, 

 Formaldehyde and Zenker's fluid are suitable for almost every tissue and 

 organ. F"ormalin has the advantage of having strong penetration, hence it 

 preserves whole animals fairly by immersing after filling the abdominal and 

 thoracic cavities. Formaldehyde is excellent where a study of fat is in ques- 

 tion, and it is much used as a fixer where frozen sections are desired (\ 43S). 

 Remember the necessity of removing mercury from sections of tissues fixed 

 with a mercuric fixer (5 473,477). 



\ 431. Mechanical Preparation of Tissues etc. for Microscopic Study. -- 

 A limited number of objects in nature are small enough and transparent 



