90 CHAPTER VII. 



Jtfifc., ix, 4, 1893, p. 445, and in Journ. Roy Mic. Soc., 1893, p. 706; and 

 a description of some later improvements in Zeit.f. wiss. Mik., xv, 1, 1898, 

 p. 23, or Journ. Roy. Mic. Sue., 1899, p. 106. 



125. Imbedding Methods. The processes known as Im- 

 bedding Methods are employed for a twofold end. Firstly, 

 they enable us to surround an object, too small or too delicate 

 to be firmly held by the fingers or by any instrument, with 

 some plastic substance that will support it on all sides with 

 firmness but without injurious pressure, so that by cutting 

 sections through the composite body thus formed, the in- 

 cluded object may be cut into sufficiently thin slices without 

 distortion. Secondly, they enable us to fill out with the im- 

 bedding mass the natural cavities of the object, so that their 

 lining membranes or other structures contained in them may 

 be duly cut in situ; and, further, they enable us not only to 

 surround with the supporting mass each individual organ or 

 part of any organ that may be present in the interior of the 

 object, but also "to fill out or impregnate with it each separate 

 cell or other anatomical element, thus giving to the tissues a 

 consistency they could not otherwise possess, and ensuring 

 that in the thin slices cut from the mass all the minutest 

 details of structure will precisely retain their natural relations 

 of position. 



These ends are usually attained in one of two ways. Either 

 the object to be imbedded is saturated by soaking with some 

 material that is liquid while warm and solid when cold, 

 which is the principle of the processes here called Fusion 

 Imbedding Methods ; or the object is saturated with some 

 substance which whilst in solution is sufficiently fluid to 

 penetrate the object to be imbedded, whilst at the same 

 time, after the evaporation or removal by other means of its 

 solvent, it acquires and imparts to the imbedded object 

 sufficient firmness for the purpose of cutting. The collodion 

 process sufficiently exemplifies this principle. If a piece of 

 soft tissue be dehydrated, and soaked first in ether and then 

 in collodion, and if the ether contained in the collodion be 

 allowed slowly to evaporate, the tissue and mass of collodion 

 which penetrates and surrounds it will acquire a consistency 

 such as to admit of thin sections being cut from them. The 

 methods founded on this principle are here called Evaporation 

 Imbedding Methods. 



