BY ARTIFICIAL MEANS. 151 



It often happens that in the rough sowings you may introduce 

 into the liquids with the Diatoms algae, or spores of algge, of 

 protococci, desmids, confervas, etc. ; more rarely in the liquids I 

 have described, cryptogams of the moss tribe increase very annoy- 

 ingly, but the green algae are the most troublesome, and if you 

 cannot eliminate them, they will pervade the whole liquid, taking 

 up rapidly the organic and mineral substances contained in the 

 maceration, and the life of the Diatoms will be rendered 

 impossible. 



If the Infusoria (properly so called) are of but little injury to 

 the Diatoms, we cannot but consider as dangerous some of the 

 Parameceae, which will swallow as they pass, in their gluttony, a 

 little navicule, a cyclostella, or an achanthe ; nor can we say 

 otherwise of a class of Protozoons — the Rhizopods — which, like 

 the Vampyrellas, destroy them one by one, and spoil the growth. 

 I have in my laboratory a kind of Actinophrys, which, sown along 

 with the Diatoms, in a maceration highly nutritive for siliceous 

 algae, disorganised and killed them by enclosing them for a long 

 time in its protoplasmic mass. The Glass Worm, and many 

 other annelides, also spoil the growth of Diatoms, but it is easy 

 to get rid of them by killing them. 



The Bacteria, as previously said, also attack the Algae that we 

 are growing, and it is not rare, even in the most successful 

 grovvths, to distinguish moveable friistules perfectly endochromed, 

 literally covered with the filaments of Bacteria, fixed perpendicu- 

 larly on^the thallus, giving them the appearance of cells bristling 

 with pseudopodia. When the medium is very favourable to the 

 production of schizomycetes, all the Diatoms are tainted with the 

 bacillus disease ; they end by becoming immovable, their valves 

 open out, and then parasites of all sorts settle down on their 

 endochrome, which is destroyed in a few days ; and the Protozoa 

 make only a few mouthfuls of this protoplasm which has become 

 accessible to them, and in a very little time the Diatoms are 

 entirely ground up. 



Without being directly attacked, Diatoms are also pathologic- 

 ally influenced by the proximity of many cryptogams. I know 

 one moss that, grown by the side of these algse, induces among 

 them a kind of " melanose," or " anthracnose," manifesting itself 



