CARMINE AND COCHINEAL 143 



added. 11' teasing is required, this is now done. A thin cover- 

 slip is then placed over the material which is allowed to stain 

 from a few minutes up to half an hour or more, depending on the 

 sample of stain and the tissue. The excess stain is drawn off with 

 filter paper and the tissue is crushed so that the cells will not be 

 more than a few layers thick. All excess stain is now blotted off, 

 and the edge of the coverslip may be sealed with vaseline, melted 

 parafthi or even thick damar. If only a temporary mount is wanted 

 the sealing can be omitted, since a well-made aceto-carmine slide 

 will keep well for a few hours without sealing. 



Aceto-carmine has proved to be an exceedingly valuable 

 cytological reagent for a study of chromosomes in fresh tissues. 

 It fixes and stains the chromosomes at the same time, so that they 

 may be studied at once without recourse to the ordinary methods 

 of preservation and sectioning. For making chromosome counts 

 and for a study of the morphology of the metaphase chromosomes 

 either in mitosis or meiosis, it is excellent. Recently, several 

 different methods have been devised for making permanent 

 mounts of aceto-carmine preparations. While in the writer's 

 experience these are not quite as brilliant as fresh slides, they are 

 entirely satisfactory for all but the most detailed type of 

 observation. 



Too much emphasis cannot be placed upon the fact that the 

 successful use of aceto-carmine depends upon having the proper 

 grade of powdered carmine to begin with. Unfortunately, there 

 is no method by which we can test the carmine except its use. 

 If the reader experiences unsatisfactory results he is advised to 

 try other samples of carmine. 



The study of aceto-carmine mounts is facilitated if the observer 

 will use a blue-green filter for artificial light. For the 6-volt 

 research lamp in common use in America, the Zeiss B-G No. 7 filter 

 will be found excellent when used with a frosted glass screen. 



Methods for Making Permanent Aceto-Carmine Slides 



McClintock {Stain Technology, iv, 1929, p. 53) first preserves 

 plant material in acetic-alcohol. The contents of anthers are 

 squeezed out on a slide in a few drops of Bclling's aceto-carmine 

 and covered. The slide is heated over an alcohol lamp for a 

 second, repeating four or five times. Now place the slide in a 

 Petri dish containing 10 per cent, acetic acid, until the coverglass 

 will come free. Then pass the slide and the coverglass separately 

 through the following solutions : 1 part glacial acetic acid and 3 

 parts absolute alcohol ; then 1 part of acetic and 9 of absolute 

 alcohol ; and then absolute alcohol. From this it is passed through 

 xylol and the slide and cover are reunited in damar or balsam. 



Steere {Stain Technology, vi, 1931, p. 107) makes smears 

 of fresh anthers, stains these in stcammg iron aceto-carmine for 



