ON A EED PIGMENT-FORMING ORGANISM. 411 



any extraneous body, and forms delicate, slightly resistant, 

 gelatinous films. The organism in these films does not appear 

 to have any distinct morphological peculiarities. There is a 

 decided tendency to the formation of a gelatinous material 

 round the cells in the cultures on solid matter, especially on 

 potato. 



On potato the growth is copious and the colour well de- 

 veloped. The organism forms a raised irregular waxy-looking 

 coating with a bright reflecting surface. The growth is gela- 

 tinous, adherent to the surface of the potato, and the colour 

 is much the strongest in the superficial layers. A greyish 

 blue discoloration of the potato occurs round the growth, 

 appearing early but subsequent to the development of the red 

 pigment, and obviously connected with the growth of the 

 organism. The potato acquires within the zone of grey pig- 

 ment a slight alkaline reaction, but no distinct odour is de- 

 veloped, as in the case of M. prodigiosus. In old potato 

 tube cultures the pigment becomes a pale chocolate-brown. 



Temperature. — ;The organism grows well at the ordinary 

 temperature, and has its optimum between 20° and 23°. Above 

 this the growth is slower, and at 37° ceases, but the cultures 

 grow rapidly again on removal to a lower temperature. 

 Exposure for one hour to a temperature of 60° kills tlie 

 organism. Simple drying at 37° ou a cover-glass does not 

 impair the vitality. 



Pigment. — The pigment in this organism is largely con- 

 tained in the cells, and is not an excretion. It cannot be ex- 

 tracted by simple shaking with water, ether, alcohol, or chloro- 

 form, but requires to be first liberated by disruption of the 

 cells by boiling. It is set free by boiling in water, but is not 

 dissolved. Alcohol and chloroform dissolve it easily, but 

 ether does not. It has not been obtained in a crystalline form. 

 When acted ou by alkalies it is turned a yellowish brown, and 

 this is probably the reason of the change of colour in old potato 

 cultures. Acids restore the colour aff'ected by alkalies, but do 

 not themselves cause any change in the original pigment. 

 With the spectroscope no absorption hands could be detected, 



