628 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [22] 



I do not see what else can be desired. The method which has gi veu good 

 results in the haudsof the writer has already been described, and dift'ers 

 but little from the method commended by Brass. Sections of the most 

 extreme thinness can be cut by its use, Blitschli having succeeded, 

 with small specimens, in getting sections measuring only .002"'°» or about 

 iYsiTo ^^ '^^1 uich in thickness. 



Oomhined killiHg, staining, and preservative agents. — To this category 

 we may assign such combinations as amraonio-picro-carmine, borax- 

 picrocarmine, and picric acid combined with nigrosin prepared accord- 

 ing to the formula of Pfitzer. The preparation of ammonio-picro-car- 

 mine is attended with a good deal of trouble and takes a great deal of 

 time and attention if some of the formulae which have been proposed 

 are followed in its preparation. 



The readiest way of preparing a picro-carmine, I find, is to have a stock 

 solution of borax-carmine on hand which may be poured into a saturated 

 solution of pid'ic acid in sufficient quantity to give a deep orange-red 

 mixture which may then even be combined with a small percentage of 

 alcohol. In this way we obtain a staining mixture which dyes small 

 objects, such as embryos, with two colors in different parts, and is also 

 a temporary preservative, killing, and hardening mixture. The objects 

 after a day or two are removed from this mixture and put into 30 to 40 

 per cent., and finally into 70 per cent., alcohol. 



Pfitzerh mixture of picric acid and nigrosin has been commended in 

 botanical research ; but it appears probable from a little experience 

 which I have had with it that it will be useful in animal histology. A 

 few drops of a watery solution of nigrosin are mixed with a saturated 

 solution of picric acid; this mixture has an olive green color; it kills 

 quickly and stains the granules and nuclei beautifully, imparting to 

 them a tint somewhat similar to that i^roduced by hsematoxjiin. 



Fixing sections upon the slide preparatory to mounting. — This T find may 

 be very easily done by the aid of Schallibaum's mixture of oil of cloves 

 and collodion. 



Collodion 1 volume. 



Oil of cloves 3 to 4 volumes. 



The slides are thinly painted with this mixture over the center whore 

 the sections are to be placed with a perfectly clean camel's-hair pencil. 

 The sections which are cut by the dry method are lifted from the upper 

 side of the section knife as fast as cut, and laid on the slide in serial 

 order. If a section stretcher or flattener is used on the knife the sec- 

 tions may be lifted ofl" in short ribbons consisting of several consecutive 

 sections sticking together, edge to edge. After the sections have been 

 neatly arranged in successive rows, and in serial order from left torigl^t, 

 with the aid of a needle, the slide may be gently warmed over an alco- 

 hol lamp, when the i)araffine will melt and let the sections drop down 

 and sink into the film of collodion and clove oil. By warming the slide 



