CHAPTER XXIII. 



MAOEEATION, DIGESTION, AND CORROSION. 



Maceration. 



520. Methods of Dissociation. — It is sometimes necessary, in 

 order to obtain a complete knowledge of the forms of the 

 elements of a tissue, that the elements be artificially sepa- 

 rated from their place in the tissue and separately studied 

 after they have been isolated both from neighbouring ele- 

 ments and from any interstitial cement-substances that may 

 be present in the tissue. Simple teasing with needles is 

 often insufficient, as the cement-substances are frequently 

 tougher than the elements themselves, so that the latter are 

 torn and destroyed in the process. In this case recourse 

 must be had to maceration, by which is meant prolonged 

 soaking (generally for days rather than hours) in media 

 which have the property of dissolving, or at least softening, 

 the cement substances or the elements of the tissue that it 

 is not wished to study, whilst preserving the forms of those 

 it is desired to isolate. When this softening has been 

 effected, the isolation is completed by teasing, or by agitation 

 with liquid in a test-tube, or by the method of tapping, which 

 last gives in many cases (many epithelia, for instance) results 

 which could not be attained in any other way. The macerated 

 tissue is placed on a slide and covered with a thin glass cover 

 supported at the corners on four little feet made of pellets 

 of soft wax. By tapping the cover with a needle it is now 

 gradually pressed down, whilst at the same time the cells of 

 the tissue are segregated by the repeated shocks. When the 

 segregation has proceeded far enough, mounting medium may 

 be added and the mount closed. 



A good material for making wax feet is obtained (Vosselee, 

 Zeit. wiss. Mih., vii, 1891, p. 461) by melting white wax and 

 stirring into it one half to two thirds of Venice turpentine. 



