738 SUMMABY OF CURRENT RESEARCHES RELATING TO 



This obstacle may be entirely avoided by the proper use of 

 collodion. 



We are indebted to Mason,* so far as I am aware, for tbe first 

 suggestion of tbe use of collodion in this connection. But the method 

 employed by Mason has serious objections. A drop of collodion on 

 the surface of a paraffin-imbedded preparation softens the object to 

 such an extent that cutting is a very slow process, and thin sections 

 are not easily attainable. The thickness of the collodion film, more- 

 over, interferes more or less with accurate study of the mounted 

 object, even if the sections are inverted when applied to the slide. 

 The gradual drying of the surface of the film also causes the section 

 to roll into a hollow cylinder with its collodion surface innermost, so 

 that the inversion of the section becomes difficult, if not altogether 

 impossible. The consistency of the collodion to be used is stated by 

 Mason, but this is of little value, since even a short exposure to the 

 atmosphere often repeated will quickly change the condition of the 

 collodion in the bottle. 



All these impediments — but for which, I believe, the method 

 would have come into more general use — may be largely if not entirely 

 obviated by using a very small amount of a rather thin collodion. 



The criterion which serves me is : the collodion must dry almost 

 instantly (within two or three seconds after being applied) without 

 leaving a trace of glossiness on the surface of the paraffin.^ 



In this collodion process I use at present the following method : — 



The object, imbedded in paraffin in the ordinary way, is placed in 

 a receiver of a Thoma's microtome and the paraffin cut away to within 

 1 mm. to 2 mm. of the object on four sides, leaving a rectangular 

 surface of paraffin, two edges of which are parallel to the edge of the 

 knife. 



A slide prepared by being painted with a thin coat of Schallibaum's 

 mixture of collodion and clove-oil is placed at the left of the micro- 

 tome. 



At the right of the latter, handy to the right hand, is a small 

 bottle half-full of the thin collodion, into which dips the tip of a 

 camel's-hair brush ; the quill of the brush is thrust through a hole in 

 a thin flat cork, which serves at once as a temporary cover to the 

 bottle and a support to the brush, the latter being adjusted to any 

 height of the collodion by simply pushing it up or down through the 

 bole in the close-fitting cork. Near by is a small bottle of ether, with 

 which the collodion is thinned as soon as it begins to leave a shining 

 surface on the paraffin. 



The operator should sit facing the light, so that he may judge 



* N. N. Mason, ' Use of Collodion in cutting thin Sections of Soft Tissues, 

 Amer. Natural., xiv. (1880) p. 825. 



f Judging from the effects, I am inclined to think that by this method the 

 collodion penetrates the preparation to a certain depth, fixing the parts in their 

 natural relations without producing a superficial film. At any rate, if the 

 sections are made sufficiently thin (e. g. 5 ii) there is no curling, whereas -with 

 much thicker sections, the superficial portion of which alone contains in that case 

 the collodion, there is often a tendency to roll. This I have attributed to the 

 slight shrinkage in the upper or collodion-impregnated portion of the section. 



