CHAPTER XXIII. 



9 



MACERATION, DIGESTION, AND CORROSION. 



Maceration. 



512. 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 separated from their 

 place in the tissue and separately studied after they have been 

 isolated both from neighbouring elements 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 mace- 

 rated 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 (VossELER, 

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

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



The most desirable macerating media are those which, whilst 

 dissolving intercellular substances, do not attack the cells them- 

 selves. Those which contain colloids have been found to give the 

 best results in this respect. Iodised serum is an example. 



513. Iodised Serum (Chap. XIX.). The manner of employing it 

 for maceration is as follows : A piece of tissue smaller than a pea 



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