150 SUMMARY OF CURRENT RESEARCHES RELATING TO 



absolute alcohol the preparations were cleared with bergamot oil or 

 xylol, imbedded in paraffin, which was removed by xylol, and put up in 

 Canada balsam to which xylol had been added. Xylol is to be preferred 

 to such fluids as turpentine or chloroform. 



Preparing Moulds.* — Mr. E. B. Wilson considers that although it 

 is well known that the study of moulds may bo greatly facilitated by 

 following their development in gelatin films, or other solid substrata, 

 spread on glass slides, yet that the value of the method for classes in 

 elementary biology has not been suflicicutly recognized. He therefore 

 calls attention to the following application of the method, as simple and 

 practical, and especially as affording a ready means of making very clear 

 and beautiful permanent preparations. 



The spores are sown with a needle-point in films, consisting of a 

 modification of Pasteur's or Mayer's fluid (with pepsin) thickened with 

 Iceland moss. In this medium moulds grow freely in the moist-chamber. 

 They may be examined either fresh or after treatment with iodine, 

 which scarcely colours the substratum. For the purpose of making 

 permanent preparations the culture-slides arc transferred directly from 

 the moist-chamber to a saturated solution of eosin in 95 per cent, 

 alcohol, a fluid by which the moulds are at once fixed and stained. 

 After twenty-four hours (or, preferably, three or four days), the pre- 

 parations are washed in 95 per cent, alcohol until the colour nearly dis- 

 appears from the substratum, cleared with oil of cloves, and mounted in 

 balsam. All stages may thus be prepared. The mycelia, conidia, &c., 

 appear of an intense red colour, while the substratum is scarcely stained. 

 Alcoholic fuchsin may be used instead of eosin, though inferior to it ; 

 but other dyes (of which a considerable number have been tested) colour 

 the substratum uniformly with the moulds, and are therefore useless. 

 Eosin preparations made more than a year ago do not yet show the 

 slightest alteration of colour. The best results have thus far been 

 obtained with Penicillium, Eurotium, and certain parasitic forms. Mucor 

 gives less satisfactory preparations, since it is always more or less 

 shrunken by the alcohol. Fair preparations of yeast may be made by 

 mixing it with the liquefied medium and spreading the medium on glass 

 slides, which, after solidification of the films, are placed in the eosin 

 solution, as in the case of mould-cultures. 



For preparing the cultures, Pasteur's or Mayer's fluid, with pepsin 

 (see Huxley and Martin's ' Practical Biology '), but not containing more 

 than 5 per cent, of sugar, is heated with Iceland moss until the mixture 

 attains such a consistency that it will just solidify when cold (fifteen to 

 thirty minutes). It is then filtered by means of a hot filter into small 

 glass flasks, which are afterwards plugged with cotton-wool, and steri- 

 lized at 65° to 70° C. by the ordinary method. When required for use 

 the mass is liquefied by gentle heat, poured on the slides, and allowed 

 to solidify. The spores are sown by a needle-point, touched once to a 

 mass of spores, and thereupon drawn across several films in succession, 

 the spores being thus scattered along the track of the needle, and more 

 or less completely isolated. Care must be taken that the quantity of 

 sugar be not too great. The films should be tolerably thick, and the 

 atmosphere of the moist-chamber such that the films neither dry nor 

 liquefy. 



* Amer. Natural., xxi. (1887) pp. 207-8. 



