Post-fixation Treatments 23 



out blood ahead of the fixative. (2) If the head alone is to be fixed, clamp 

 off the thoracic duct, and if the brain and spina! cord are to be fixed, 

 clamp off intestinal vessels. The fixative is then directed toward brain 

 and spinal cord. (3) When the perfusion bottle is being filled, allow 

 some of the fluid to flow throug^h the rubber tubing and cannula to 

 release air bubbles. This can also be done wath the saline. Air bubbles 

 will block the perfusion. (4) Do not allow the injection pressure to ex- 

 ceed the blood pressure; artifacts will result. 



If only a small piece of an organ is to be fixed, a modified and easier 

 perfusion may be undertaken. Inject the organ with a hypodermic syr- 

 inge of fixative. This usually will be found adequate. Immediately after 

 injection, cut out a small piece of tissue close to the injection and im- 

 merse in the same type of fixative. 



Lillie {1954B) lists two disadvantages of perfusion: the blood content 

 of the vessels is lost and perfusion cannot be used if post-mortem clot- 

 ting is present. But he does favor perfusion as the oiustanding method 

 for brain fixation, saying that immersion of the whole brain without 

 perfusion "can only be condemned." If whole brain perfusion is not 

 possible he suggests the following as the preferred method of fixation 

 for topographic study. 



1. Cut a single transverse section anterior to oculomotor roots and interior 

 margin of anterior colliculi, separating the cerebrum from midbrain and 

 hindbrain. 



2. Make a series of transverse sections through the brain stem and cerebel- 

 lum (5-10 mm. intervals) leaving part of meninges uncut to keep slices in 

 position. 



3. Separate two cerebral hemispheres by a sagittal section. On sagittal surface 

 identify points through which sections can be cut to agree with standard 

 frontal sections. Make cuts perpendicular to sagittal surface. Cut rest of 

 brain at 10 mm. intervals. 



4. Fix in a large quantity of solution. 



References: Bensley and Bensley (1938); Cowdry (1952); and Lillie 

 (1954B). See also Koenig et al. (1945) and Eayrs (1950). 



Post-fixation Treatments 



Chromatization 



2.5-3% aqueous potassium dichromate (2.5-3 gm./lOO ml. water): 

 overnight for small gross specimens (l-2cm.), 2-3 days for larger 



