184 TEXT-BOOK OF BACTERIOLOGY. 



One of these latter is a small, fine bacillus without any power of 

 spontaneous movement. 



On the glass plate it forms large, iridescent colonies, with jagged 

 edges, which, under the microscope, appear as light yellow, delicate 

 disc-like plates, and display very fine, elegant, leaf-like markings. 

 In the centre one often sees a darker speck from which the colony 

 began. In the test-tube it grows almost entirely at the surface; 

 the puncture remains sterile. A tender, circumscribed growth 

 takes place with irregular edges, which permeates the gelatin for 

 some distance with a beautifully gleaming, iridescent pigment. 



The other non-liquefying bacterium is also a bacillus, but with 

 the power of spontaneous movement, much larger than the one 

 just treated of, and characterized by its forming large central 

 spores which possess a peculiar, strongly-red gleam and glitter. 

 This ma} 7 , under some circumstances, be so striking that one is 

 led to suspect at first sight that it has been stained with fuchsin. 

 It has, therefore, been described as Bacillus erythrosporus. 



On the glass plate and in the test-tube it grows like the previ- 

 ous species, only that its colonies do not show the same beautiful 

 markings, and that some growth occurs in the puncture, at least 

 in the upper portion of it. The production of the iridescent color- 

 ing matter proceeds just as in the last-mentioned species. 



All these water-bacteria have certain qualities in common : they 

 are all aerobic species, which are distinguished by particular sensi- 

 tiveness to any want of oxygen; they will not thrive at high tem- 

 peratures, which, of course, prevents them from developing any 

 pathogenic qualities; lastly, they" find in ordinary water, without 

 any addition of nutriment, all the requisite conditions for their 

 growth and propagation, and thus their unpretending nature may 

 even, under some circumstances, enable them to live in water that 

 has been repeatedly sterilized and distilled, and thus to subsist on 

 a quantity of organic substance so small that it may be said to 

 hardly exist at all if judged by our ordinary standard. 



PHOSPHORESCENT BACTERIA. 



The water of the sea is likewise the home of a special group of 

 micro-organisms, which have become known to us chiefly through 

 the investigations of B. Fischer. They all possess the capacity of 

 shining in the dark, they are phosphorescent, and in artificial cul- 

 tures this peculiar phenomenon is readily observed. 



We know at the present time three different species of bacteria 

 which glow in the dark. One, called Bacillus phosphorescens by 



