274 



an insufficient food and on a broth-agar plate it develops but poorly. This changes 

 however by adding a good carbon source. If this is done locally on a broth-agar plate 

 there results an auxanogram in the diffusion circle of the related matter, which proves 

 at the same time that the other elements required for the growth of Oidium, as 

 potassium, magnesium and phosphor, are present in sufficient quantity in the broth. 

 As these elements accumulate in the young cells, either as the same chemical com- 

 pound found in the substrate or not, such experiments are apt to demonstrate the ab- 

 sorption phenomenon formerly described by me. It is also easy in reversing the 

 experiment, that is by feeding with carbohydrates, to find with the microscope by 

 means of iodine, glycogen accumulated in the so large Oidium cells and its disap- 

 pearing in the auxanograms of nitrogen food, such as ammonium salts or urea, as soon 

 as the carbon food in the substrate is wholly assimilated. 



A feebly acid reaction of the medium furthers the growth of Oidium, and 

 organic acids, for example acetic and lactic acid, may disappear by oxidation. Other 

 acids as molybdenic and tungstic acid are in good media, such as glucose-broth-agar, 

 reduced by Oidium to the well-known blue oxides, which gives rise to beautiful 

 colour experiments. In neutral solutions the salts of these acids are however not 

 affected so that this is a case of reduction in an acid medium. The ordinary alcohol 

 veasts behave likewise. 



Use of the milkmould for the pure culture of anaerobes. 



In nature the withdrawing of oxygen from the environment, which is required 

 for the development of anaerobes, is usually caused by aerobic, microbes. 



They not only absorb the last traces of oxygen from the surroundings but even 

 produce reducing substances in it. In the laboratory this may be imitated by adding 

 to a culture medium containing in small number germs of the anaerobe to be exa- 

 mined, a great number of germs of an appropriate microbe. How such experiments 

 have hitherto been carried out *) may be illustrated by a definite example namely the 

 cultivation of the spore-forming aerobes of the albumin putrefaction ; then I will 

 describe the modified method. 



A crude culture of putrefaction bacteria is obtained thus. A stoppered bottle is 

 quite filled with a watery infusion of albuminous matter, infected with garden soil 

 and boiled to kill all non-sporogenous microbes. Placed in the incubator the mass 

 soon passes into stinking putrefaction, characteristic by the presence of mercaptans 

 produced by the spore-forming anaerobes. Now to ordinary broth-gelatin or broth- 

 agar an abundant quantity of some intensively growing aerobic bacterium, such as 

 B fiuorescens or B. prodigiosum is added, together with a little of the to 90 or 

 1 00 C. heated material containing the spores of the putrefaction microbes. After 

 solidification in a test tube the aerobes near the bottom will soon absorb the last traces 

 of oxygen and being unable to grow there, not give rise to liquefaction of the gelatin ; 

 but they will retain the oxygen penetrating from above and develop strongly in the 

 surface of the gelatin. In the lower part of the tube the spores of the putrefaction 



') E. Mace, Traite pratique de Bacteriologie, 6e Ed. T. I, pag. 305, Paris 1912. 

 Besson, Technique microbiologique et serotherapique, 6e Ed., pag. 102, Paris 1914. 



