" WATER TURNED TO BLOOD. 207 



The degree of concentration of the water has a marked influence 

 on them. On the 1st October, 1839, after the driest summer on record, 

 the liquid in the tables indicated 25° salinity in Baume's areometer, 

 and it was of so deep a color as to stain a corner of my pocket-hand- 

 kerchief a blood-red. On October 28th, after twenty-eight days of 

 steady rain, the water in the pieces mattresses, instead of presenting a 

 purple color, as on the first day of the month, resembled blood with a 

 very large amount of serum, and the monads in it were less numerous, 

 and of a lighter red, although the water was still of 20° salinity. 



Finally, we must not omit to state that the monads are very sen- 

 sitive to light, which they seek with a certain degree of avidity. This 

 may be easily seen by putting a number of these infusoria into a flask 

 two-thirds filled with sea-water. Soon they will be seen to rise to the 

 surface of the liquid, and to crowd together on the side where the 

 light is strongest. If the flask be turned about so as to bring them 

 on the darker side, they soon take their former position again. We 

 must also observe that these animalcules sometimes go down to the 

 bottom of the tables, and then the coloration of the surface grows 

 fainter, or entirely disappears. 



From all this it follows that the red color of the Mediterranean 

 salt-marshes is caused by the Monas Dunalii ; but is that animalcule 

 the only cause of the phenomenon ? Has not the Artemia salina of 

 Audouin, Dumas, and Payen, also something to do with it ? This 

 problem was soon solved. We have first to bear in mind that these 

 little crustaceans are found in far greater numbers in brackish water 

 than in water at its maximum point of concentration, and that in the 

 latter case, indeed, they occur so rarely that their presence may be 

 regarded as in some sort merely accidental. In water of this kind, the 

 artemia appears to be sickly ; it evidently languishes in the over-dense 

 medium ; it swims about with difficulty, always keeping at the surface. 

 It is more or less of a red color along the line of its digestive canal ; 

 but this coloration is a secondary thing, and is owing to the monads 

 it has swallowed in water. The latter deposits in their intestine salt- 

 crystals, which may be seen through their transparent envelope, min- 

 gled with monads in a state of partial or total digestion. 



Far, then, from being the cause of the purple tint of salt-water in 

 its last stage of concentration, the artemia is indebted for its accidental 

 coloring to the Monades Dunalii it takes into its digestive canal, or 

 which settle among the filaments of its branchial feet. This I have 

 demonstrated by keeping colorless artemiae for a while in water tinged 

 by red monads, or simply by carmine, and so giving them a red color. 



But, though the artemia has nothing to do with the coloration of 

 water, it is, nevertheless, a subject of wonder and study for the physi- 

 ologist. Like several other animals belonging to the great sub-king- 

 dom Articulata (psyche, bee, silk-worm moth), our crustaceans possess 

 the singular privilege of reproducing themselves without being sub. 



