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tioning. Many methods designed to accomplish the same purpose have 

 been described and used, but for rapidity, ease of manipulation, and 

 accuracy of results, few are equal to the method described by Patten. 



For some kinds of objects, more especially small embryos, this 

 method has proved somewhat troublesome, as such embryos are not 

 easily picked from a dish of oil on the end of a knife blade, and even 

 when this is accomplished it is not easy to drain off the excess of oil and 

 leave the embryo in such a position that it can easily be transferred 

 to the collodion mixture on the paper. 



To avoid these difficulties, some workers have depended upon 

 smearing the paper, or strips of tracing linen, with the collodion mix- 

 ture, and dropping the embryos on it with a dropping tube ; care being 

 taken to transfer as little oil as possible. 



This method frequently gives trouble. 



In the first place it is not possible to accurately place more than 

 one object in each drop of oil. A needle moved about in the oil is all 

 that is necessary to move all of the embryos in its vicinity. 



There is another, and a very strong objection to this method. Con- 

 siderable collodion must be used on account of the excess of oil. If 

 the embryo is allowed to sink well into the collodion, it will adhere 

 firmly to the paper and will not come off in the paraffin. If on the 

 other hand the embryo does not settle on the collodion, it will not stick 

 to the paper at all, but will come off when transferred to turpentine. 



I find that these difficulties may be overcome by draining the ex- 

 cess of oil away on an inclined plane of tracing linen, that has been 

 oiled with oil of cloves so that the oil will flow readily, sliding them off 

 the edge of the linen, one at a time, with a knife blade or a spear 

 pointed needle, and then transferring to the collodion. 



In order that the reader may understand all of the steps, I will 

 describe the process from the beginning, as I now use it in embedding 

 embryos. 



Embryos are run through the grades of alcohol in the usual way, 

 and cleared in oil of cloves. It is important that oil of cloves or some 

 other oil that readily dissolves collodion be used. In most cases it is 

 convenient to have the embryos lightly stained with some transparent 

 stain, so positions can be accurately determined. 



Take a piece of tracing linen, such as is used by civil engineers 

 for map tracing, about four centimeters square, and crease it through 

 the middle so that the two sides of the glazed surface form an obtuse 

 angle. Oil this linen well with oil of cloves and lay it on a slide so 

 that the cloth surface of one side is held to the slide by the oil. 



With a dropping tube, draw up a number of the embryos, now in 

 oil of cloves, and drop them along the upper edge of the inclined plane 

 of the linen, fig. 1. The oil will run down the linen and leave the em- 

 bryos stranded. Unless the embryos are much more delicate than the 



