RECENT RESEARCHES INTO THE HISTORY OF BACTERIA. 267 



mikrom. ; nothing could be seen of them save a pale red sub- 

 stance, in which were embedded darker granules ; even cilia 

 could not be seen. Their swarming movement was quite distinct 

 from the ordinary trembling molecular movement, and it was 

 due to it that they were enabled to collect themselves in 

 groups on that side of the vessel which was turned to the 

 light. Cohn thinks this form to be identical with that 

 described by Ehrenberg in his ^ Infusions-thierchen,' p. 11, 

 in 1838. Charles Morren observed it, and gave an account 

 of it to the Academy at Brussels in 1841, as forming the wine- 

 red palmelloid crusts, which often extend to several inches in 

 breadth, over water in which Pteris aquilina is decaying.^ 

 Perty^s form Chromatium (Monas) violescens, Cohn thinks is 

 probably the same as that described by himseU as M. vinosa. 

 8. Monas Okenii{(ig. 12). Specimens of this form, which 

 were also made known to science by Ehrenberg, were obtained 

 through Dr. Hirsch, of Kahla in Thuringia, from a very rich 

 pond in that place, the water of which was coloured red ; the 

 cause of this was the presence of a short cylindrical organism, 

 ordinarily twice or three times as long as it was broad, with 

 a diameter of *005 mm., and a long axis varying from 

 •0075 to '015 mm., according to the state of division in which 

 it was found, with the ends rounded and generally slightly 

 bent. It was found in enormous quantities, turning slowly on 

 its axis ; with this period of activity there alternated one of rest; 

 they were mostly to be found on the side of the glass which 

 was turned to the light; at first no organ of movement was seen, 

 but the addition of iodine solution brought out a very long 

 flagellum of more than twice the length of the body, behind 

 which it was carried straight, or bent spirally. Just as in his 

 Clathrocystis, Cohn found a varying number of dark granules 

 in the interior of the organism ; if one be dried, and alcohol 

 added, the granules become coloured, and leave the protoplasm 

 colourless, while one or two vacuoles appear in the limiting 

 membrane. Acetic acid colours them a bright red ; ammonia 

 dissolves them, and gives a brownish-red colour to the pigment. 

 These red corpuscles are the chief nourishment of the various 

 kinds of animals, found in the water which they inhabit ; 

 curiously enough, their coloration in the Rotifera gives us some 

 idea of the characters of the secretions of these animals ; in the 

 true stomach the corpuscles were of a bright red, due, as Cohn 

 thinks, to the acid reaction of the gastric juice ; while in the 

 other portions of the intestine they were of a dark or brown- 



' Mem. de I'Acad. de Bruxellcs, 1841, p. 70. 

 ' Perty, Kieinste Lebensformen, 1852, p. 174. 



