FIXING AND HAUDENING. 25 



for certain Arthropods with very resistent iuteguinenfcs) . 

 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 adniixtui-e 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 Flemming'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 tliorougli penetration 

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

 injection of Golgi, De Quervain, M^nn, and others, given under 

 Nervous System. 



Bbaus and Deitenbr {Jena. Zeit. Naturw., Bd. xxix, 1895, p. 435) 

 fix fishes hy injection through the bidbus aortie. The vessels are first 

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

 thrown in. 



Kolmee {Anat. Ana., xlii, 1912, p. 47) fixes thus even large mammals 

 (Chimpanzee, Goat). He first washes ont 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 washing 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 osmic, chromic, and platinic liquids require very thorough 

 washing out. 



It is important to use the appro'priate liquid for ivashing 

 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 



