FIXING AND HAUDKXINC. 25 



For rri'Uiin Arthropods with very resistant integuments). 



But this should only be done as a last resource. 



Let the quantity of fixing agent employed be at least many 

 times the volume of the objects to be fixed. If this precaution 

 be not observed the composition of the fixing liquid may be 

 seriously altered by admixture of the liquids or of the soluble 

 substances of the tissues thrown into it. For a weak and 

 slowly acting fixing agent, such as picric acid, the quantity of 

 liquid employed should be in volume about one hundred times 

 that of the object to be fixed. Reagents that act very ener- 

 getically, such as Fleimning's solution, may be employed in 

 smaller proportions. 



But fixation may also be performed by injection of the fixing liquid 

 into the objects, thus ensuring a more rapid and thorough penetration 

 of voluminous objects. See for this practice the methods of fixation by 

 injection of GOLGI, DE QUERVAIN, MA.NN, and others, given under 

 Nerrous System. 



BRAUS and DRUENER (Jena. Zeit. Natunv., Bd. xxix, 1895, p. 435) 

 fix fishes by injection through the bulbus aortas. The vessels are first 

 washed out with normal salt solution, and the fixing liquid is then 

 thrown in. 



KOLMER (Anat. Anz., xlii, 1912, p. 47) fixes thus even large mammals 

 (Chimpanzee, Goat). He first washes out with RINGER'S solution. 



It is well not to leave specimens in fixing liquids longer 

 than is sufficient to obtain the desired reaction. Sublimate, 

 for instance, soon makes tissues brittle. But long immersion 

 may be necessary to produce the desired optical differentia- 

 tion with some reagents. 



Careful wasldn<j out (by which is meant the removal from 

 the tissues of the excess of uncombined fixative) is necessary 

 in order to get tissues to stain properly. But it is not always 

 equally imperative. Alcohol and formaldehyde do not require 

 washing out before staining ; acetic and picric acid only for 

 some stains ; sublimate will allow of staining even if not 

 washed out, but allows of a sharper stain if well washed out ; 

 all osinic, chromic, and platinic liquids require very thorough 

 washing out. 



It is important to use the appropriate liquid for washing 

 out the fixing agent after fixation. It is frequently by no 

 means a matter of indifference whether water or alcohol be 

 employed for washing out. Sometimes water will undo the 

 whole work of fixation (as with picric acid). Sometimes 



