2 73 



v iters of distilleries and all kinds of acid sewage, are inhabited by Oidium. Natural 

 L tbitats are furthermore the sap flow of many trees caused by Cossits ligniperda and 



allies. 



For pure culture acidified malt infusion- or broth-glycerin plates are recommen- 

 dable. The acid serves to exclude the hay bacteria which have a great disposition to 

 grow in symbiosis with Oidium in neutral environment. 



The transfers for the collection are kept on malt-agar, but they change thereby 

 in a few months into a tough, leathery mycelium, almost exclusively consisting of long 

 mycelial threads difficult to separate and evenly to mix with the nutriment. To 

 obtain normal material in this case a new isolation from milk or soil is necessary, 

 for the change is an hereditary non-reversible mutation. 



Under favourable feeding conditions the growth is remarkably rapid and the 

 respiration and oxygen absorption go parallel with it. This intensity exceeds by far 

 that of the ordinary moulds of the genera Penicilliuui and Aspergillus, whilst it equals 

 that of Mucor. This holds, however, only good with regard to easily assimilable sub- 

 stances ; less decomposable matter such as pectine, cellulose and chitine are not at- 

 tacked by Oidium. Gelatin and agar are neither assimilated. Fermentation pheno- 

 mena, joined with the evolution of gas, are as said also wanting. Hence, Oidium never 

 forms rents or holes in the solid substrata wherein it is cultivated, not even in pre- 

 sence of glucose. This is one of the reasons w r hy it is so well adapted to the culture 

 experiments with the anaerobes to be discussed below. 



The products of metabolism are chiefly or only water and carbonic acid; volatile 

 or non-volatile substances noxious to other organisms are not produced. 



In regard to carbon-food Oidium exhibits a great specialisation. Most hexoses, 

 in particular glucose, levulose and mannose, are readily assimilated and oxidised. 

 Likewise aethylalcohol. Glycerin, too, is a very good carbon source. On the other 

 hand, starch, raffinose, maltose, cane sugar, mannite and all similar substances, are in 

 no way assimilated. Enzymes, as diastase, maltoglucase, invertase, lactase, are hence 

 completely absent. Glucoside enzymes could neither be found. By the absence of these 

 enzymes, Oidium, which so easily reacts on the hexoses, is especially fit as a reagent 

 on these enzymes in case they are to be detected in parts of higher plants or as pro- 

 ducts of secretion of other microbes; here the auxanographic method may advantage- 

 ously be applied. 



Fats are however split up by Oidium, by means af the exoenzymelipase, active 

 outside the cells. Hence, in presence of fats growth of Oidium may be expected at 

 ihe expense of glycerin and this explains the general occurence of Oidium as well 

 iii milk and butter as in other fat-containing materials. For the preparation of lipase 

 the milkmould can afford a good starting material. 



As to the nitrogen food Oidium resembles the ordinary yeast species and is in 

 this respect rather many-sided. With exception of nitrates and nitrites, and unchan- 

 ged albuminous substances, the ordinary nitrogen compounds are easily assimilated in 

 presence of good carbon food such as glucose and glycerin. This is in particular true 

 for ammonium salts and urea. Peptones and the higher amino acids, if alone, are not 

 or very slowly assimilated, but in presence of a good carbon source they may serve as 

 a very good nitrogen food, so that the complete nutrition of Oidium in presence of 

 these substances should be called dualistic. Consequently broth bouillon is for Oidium 



M. \V. Beijerinck, Verzamelde Geschriften; Vijfde Deel. Io 



