94 PHYSIOLOGY OF NUTRITION. 



more than eight days in a and c, while the fluids b and d 

 quickly became covered with a thick coating of mould. Grape 

 sugar and Citric acid thus serve well as food for the fungus ; 

 Oxalic acid cannot be utilised by them. In absence of organic 

 substances, no development takes place. We can test the most 

 various organic substances in the mariner above indicated as to 

 their nutritive value for Penicillium, and if it appears necessary 

 to determine quantitatively the amount of fungus produced, this 

 can be done by filtering, drying at 100 C., and weighing. 1 



To obtain pure cultures of fungi, e.g. of Mucor, Penicillium, 

 etc., we may often proceed as follows : 2 Unleavened bread, freed 

 from the crust, is heated for one to two days in the drying 

 chamber at 120 C., so as to become sterilised. We lay the bread 

 in a crystallising glass sterilised by heating, and cover this with 

 a sterilised glass plate, whose edges overhang. It is best to soak 

 the bread with a food solution. We extract dried fruits (raisins, 

 plums) with cold water, filter, and evaporate the solution to the 

 consistency of syrup. A small quantity of this is dissolved 

 in water, heated to boiling in a wash bottle, and then the bread 

 in the crystallising glass is soaked with the boiling hot fluid.* 

 We obtain the spore material by transferring some spores of, say, 

 Mucor, grown on bread or dung, to boiled water by means of the 

 forceps. After a short time, we distribute a few drops of this 

 fluid on the bread, e.g. by means of a sterilised flat needle. If 

 the culture is not yet perfectly pure, we must make a second, 

 taking the necessary spore material from the first. In preparing 

 pure cultures of fungi in food solutions, these must of coarse 

 be sterilised. The solutions contained in small flasks closed with 

 stoppers of cotton wood are sterilised by simple heating, or by 

 introducing the flasks into the steam sterilising apparatus. 



1 See Naegeli, Sitzungsberichte d. k. bayr. Akadem. d. Wiss., 1879, 

 mathematisch-pliysikalische Klasse, and Eeincke, Untersuchungen aus dem 

 botanischen Institut der Universitat Gottingen, 1883, Heft 3. 



2 See especially Brefeld, Botan. Untersuchungen iiber Schimmelpilze, Heft 4. 



36. Some Other Saprophytes. 



If stems of Vicia Faba, which have been left for a long time in 

 the fields in autumn, are soaked for several hours in spring water 



* In some cases it is necessary to neutralise the acids in the fruit extract by 

 addition of ammonia, since many fungi cannot withstand their action. 



