574 L. E. CEAWSHAY. 



But in most cases the same process was repeated as far as the experi- 

 ments were carried. 



In experiments with sterilised water, the Infusorian mostly employed 

 for inoculation w^as of the form which was referred to Strombidium, in- 

 cluding probably two, if not three, distinct species. This C^iliate, though 

 often lost sight of and superseded by smaller forms, was retained in some 

 experiments for a long period. In one case it continued fairly numerous 

 as late as the 67th day, after having cleared the water of four successive 

 cultures of Bacteria which were grown on peptone introduced on the 

 1st, 13th, 39th, and 49th days, severally. 



Following the destruction of a strong Bacteria culture by Infusoria, 

 there arises commonly, if not invariably, a more or less heavy deposit 

 of flocculent white patches in the water. The nature of this deposit, 

 possibly the excretory product of the Infusoria, was not ascertained. 

 In one experiment which had been five times impregnated with peptone 

 within a period of 29 days, a sixth impregnation of the water decanted 

 off to a clean flask on the 34th day did not produce any distinct Bacteria 

 growth, or any recurrence of the Infusoria, the w^ater remaining sickly in 

 appearance. But a similar addition of peptone to the original flask with 

 its deposit, which had been refilled with clean sterilised " outside " 

 water, produced a strong Bacteria growth, the Infusoria continuing 

 fairly numerous for some 3 wrecks later. In the former case conditions 

 had apparently arisen in the water, such as to resist further Bacteria 

 growth, the Infusoria being consequently deprived of their food-supply. 



These observations, though passing beyond the range of the subject 

 of this paper, seem to deserve notice, as emphasizing the intimate rela- 

 tionship existing, between Infusoria and Bacteria in the sea, and the 

 destructive action of the former on the latter in experiments. This 

 bactericidal action may be peculiar to certain species, or again may not 

 in these be an essential feature of their natural existence : Euplotes, for 

 example, which is rapidly destructive of Bacteria, and will apparently 

 thrive on them alone indefinitely, was at first found to be feeding largely 

 on the spores of Chlorodendron. One point seems certain, that in so far 

 as such Infusoria may occur in experiments, their presence is not in itself 

 to be regarded as nocuous, but rather, on the contrary, as an indication 

 of the presence of unhealthy conditions which they are directly engaged 

 in counteracting. 



As regards the influence of these common forms of Bacteria on the 

 experiments with the zooplankton, specimens of Calanoida and other 

 species, more especially small or young forms, were kept alive on several 



