io GENERAL MORPHOLOGY AND BIOLOGY. 



is best formed in the absence of oxygen. Sometimes the 

 faculty of forming it may be lost for a time, if not per- 

 manently, by altering the conditions of growth of an 

 organism. Thus, for example, if the B. pyocyaneus be 

 exposed to the temperature of 42 C. for a certain time, it 

 loses its power of producing its bluish pigment. Pigments 

 formed by bacteria often diffuse out into, and colour, the 

 medium for a considerable distance around. 



Comparatively little is known of the nature of bacterial pigments. 

 Zopf, who has devoted much attention to the pigments occurring in the 

 lower plants, has found that many of them belong to a group of 

 colouring matters which occur widely in the vegetable and animal 

 kingdoms, viz. the lipochromes. These lipochromes, which get their 

 name from the colouring matter of animal fat, include the colouring 

 matter in the petals of Ranunculacea?, the yellow pigments of serum 

 and the yolks of eggs, and many bacterial pigments. Among the 

 latter is a lipochrome carotin, which is also the pigment in carrots and 

 tomatoes. The lipochromes are characterised by their solubility in 

 chloroform, alcohol, ether, and petroleum, and by their giving indigo- 

 blue crystals with strong sulphuric acid, and a green colour with iodine 

 dissolved in potassium iodide. Though crystalline compounds of these 

 have been obtained, their chemical constitution is entirely unknown and 

 even their percentage composition is disputed. 



The Minuter Structure of the Bacterial Protoplasm. 

 Many attempts have been made to obtain deeper informa- 

 tion as to the structure of the bacterial cell, and especially 

 as to its behaviour in division. These have largely turned 

 on the interpretation to be put on certain appearances 

 which have been observed to occur. These appearances 

 are of two kinds. First, under certain circumstances 

 irregular deeply-stained granules are observed in the proto- 

 plasm, often, when they occur in a bacillus, giving the latter 

 the appearance of a short chain of cocci. They are often 

 called metachromatic granules (vide Fig. i, No. 16) from the 

 fact that by appropriate procedure they can be stained with 

 one dye, and the protoplasm in which they lie with another ; 

 sometimes, when a single stain is used, such as methylene 

 blue, they assume a slightly different tint from the proto- 

 plasm. The second appearance which can sometimes be 

 observed is the occurrence of rounded or oval unstained 



