INFILTRATION METHODS. 135 



two classes, distinguished by the end it is intended to compass" 

 by their employment. In the one it is merely proposed so to 

 surround an object, too small or too delicate to be firmly held 

 by the fingers or by any instrument, with some plastic sub- 

 stance 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 included object may be 

 cut into sufficiently thin slices without distortion. This is 

 simple imbedding. Its object is very easily attained in a 

 variety of ways of which the simple process of immersing the 

 object to be cut in a molten mass of some such material as 

 wax, which when cold acquires a fit consistency for the 

 cutting of thin slices, may be taken as a type. A further 

 object is proposed in the case of the other class of methods, 

 which may be designated methods of interstitial imbedding or 

 infiltration methods. In these it is proposed to fill out with 

 the imbedding mass the natural cavities of the object in order 

 that their lining membranes or other structures contained in 

 them may be duly cut in situ, or, going a step further, it is 

 proposed to surround with the supporting mass not only each 

 individual organ or part of any organ that may be present in 

 the interior of the object, but 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 details of structure will 

 precisely retain their natural relations of position. Such a 

 process of imbedding is at the same time practically a process 

 of hardening in so far as it enables us to give to tissues a 

 degree of firmness that could otherwise only be obtained by the 

 employment of chemical processes such as prolonged treatment 

 with chromic acid and the like. 



265. Infiltration Methods. The principle of the methods of 

 this second class is either, like that of the first, that by immer- 

 sion of the object to be cut in some material that is liquid 

 while warm and solid when cold, all the parts of the object 

 may be duly surrounded by the supporting mass (the second 

 class differing from the first chiefly in the employment of 

 materials possessing greater power of penetration whilst 

 liquid, in longer immersion in the liquid mass, and in such 

 previous preparation of the object, by soaking in some liquid 



