17 



Among the species of plants using some other organism as a habitat, we 

 find the formation of very different devices for the means of nutrition. Be- 

 ginning with lichens, the assistance given by thalli acquires greater and 

 greater significance, up to the formation of a mycelium. The mycelium is 

 satisfied with dead bark, or rather that attacked when dying, or with the 

 leaf substance of its host, or it can only eke out its existence when, with the 

 help of the enzyme which it excretes, it attacks the living organic substance 

 and then calls parasitism into existence. 



But in all these relations the one fundamental law becomes evident that 

 each organism is associated with the definite constitution of its substratum. 

 This substratum must have the exact requirements for satisfying all the de- 

 mands of the organism, otherwise it cannot thrive. Therefore all the organ- 

 isms which we call parasites make very definite demands on some host. How 

 narrowly limited these demands may often be is shown di recti}' by the bac- 

 teria, for which at times slight fluctuations in the amount of heat, the acidity 

 of the nutritive mixture etc., lead to the replacing of certain species by others 

 better adjusted. 



In order to cite only a few new examples we will mention the investiga- 

 tions of Thomas Milburn^ who cultivated fungi as well as bacteria. 

 Of the former he found in the case of Hypocrea rufa that an increase of 

 osmotic pressure first suppresses the formation of pigment in the conidia 

 and finally inhibits the formation of conidia. In this fungus the color of the 

 conidia changes with the reaction of the medium. If the reaction is acid, 

 green spores are formed; if alkaline, yellow spores. A well nourished 

 mycelium forms no fruit in the dark but does develop conidia when poorly 

 nourished. The yellow color of the mycelium of Aspergillus niger is very 

 sensitive to light and when exposed to it turns black within a few hours. The 

 F^acillus ruber balticus found on potatoes, the so-called "Kieler bacillus"^ 

 which, according to Laurent, forms acids on certain nutritive soils and al- 

 kalis on others, is so influenced in its production of coloring matter by the 

 nutritive substratum that it develops a violet color on an acid substratum and 

 orange red on an alkaline substratum. 



Lepeschkin"^ observed that the strictly aerobic bacteria from the 

 sputum in pneumonia. Bacillus Berestnezvi, can develop a branching growth 

 on strongly alkaline and on strongly acid substrata, but gradually acidifies 

 the alkaline substratum. In the presence of sugar (dextrose) a pinkish color 

 appears together with the disintegration of the little rods into oidia. In 

 the presence of larger amounts of nitrogen compounds (aspargin, lecithin, 

 peptone) the whole mass of bacteria turns yellow. The optimum for growth 

 l-es probably at 25°C. Even at 35°C. the bacterium grows very slowly and 

 at 38°C. is no longer able to grow. It is killed at 55°C. 



1 Thomas Milburn, Ueber Aenderungen der Farben bei Pilzen und Bakterien. 

 Centralbl. f .Bakteriologie usw. II. Division 1904. Vol. XIII. Nos. 9-11. 



2 See Breunig-, Untersuchungen des Trinkwassers der Stadt Kiel, 1888. 



3 L,epeschkin. Zur Kenntnis der Erblichkeit bei den einzelnen Organismen usw. 

 Centrabl. f. Bakteriolog-ie usw. II. Division. 1904. Vol. XII. Nos. 22-24. 



