PRESERVATION OF MATERIAL 105 



175. Carnoy's fluid. 



absolute alcohol 60 cc. 



chloroform 30 cc. 



glacial acetic acid 10 cc. 

 100 cc. 

 This is a strong fixing fluid which penetrates very rapidly, and conse- 

 quently should only be used for a few minutes, — ten to tliirty minutes is 

 probably long enough for most subjects. There is always danger of leaving 

 material too long in it. The material is washed in changes of absolute 

 alcohol until there is no odor of acetic acid, and is then best imbedded at 

 once, but may be transferred to 85% alcohol for preservation. The staining 

 of chromosomes after Carnoy's fluid is sometimes very brilliant, but spindle 

 fibers and other kinoplasmic structures are apparently less perfectly preserved 

 than by the chrom-osmo-acetic formula. 



If the subject be very resistant to penetration, as for example the mega- 

 spores of the pteridophytes, the proportionate amount of acetic acid may be 

 greatly increased. Thus two parts glacial acetic acid, one part absolute 

 alcohol, and one part chloroform have been recommended as giving good 

 results for the spores of Selaginella. However, even in these cases, long 

 treatment with medium or strong chrom-acetic acid, especially if applied 

 hot, aided by mechanical cutting or pricking of material, to assist penetration, 

 will frequently give better results than Carnoy's fluid. 



176. Concluding suggestions on fixing. It is important to facilitate mechan- 

 ically, in every way possible, the rapid penetration of the fixing fluid. Thus 

 an ovary of a lily should be pared along the angles and then sliced in pieces 

 three eighths of an inch thick or cut lengthwise. Small objects, such as fila- 

 mentous algse, may be examined at various stages in the process of fixation 

 to see if the cell contents are in good condition. Material that must be sec- 

 tioned cannot, however, be so easily observed, and shrinkage may occur, 

 which was not caused in the fixing, but at some later stage in the manipula- 

 tion leading to sectioning or staining. Consider results critically, and when 

 unsatisfactory attack the problem as one of physics and chemistry, and find 

 just where the methods failed. Close attention to these details will soon 

 give a sure command of a few simple methods of fixing which are likely to 

 give satisfaction. 



THE PRESERVATION OF MATERIAL 



177. Alcohol. Material collected for general morphological study may be 

 placed at once in 95% alcohol. It must later be transferred to a lower grade, 

 such as 70%, or it will become very brittle. Alcohol mixed with glycerin, 

 half and half, or one fourth glycerin, will keep material from becoming 



