374 K. .1. AIJ.EN AND K. \V. NELSON. 



Entei'omorplia, Vttucheria, and unicellular algse are the 

 commonest forms. The large seaweeds, such as Fucus and 

 Laminaria, do not live long if introduced. Plankton 

 diatoms, although a great number must be pumped up when 

 the reservoirs are being filled, are not represented. 



As in the case of outside water, a sample of '* tank-water," 

 inoculated from a persistent culture, will only give a very 

 small growth, minute forms, etc., soon multiplying and 

 choking out the plankton form. The ultimate growth of 

 minute unicellular algte other than diatoms is often con- 

 siderable, and many quite unknown and unidentified forms 

 have been obtained. The total growth of vegetable forms is 

 always found to be greater than iu the case of outside water. 



In cultures of plankton diatoms made with sterilised tank- 

 water, a very great improvement on outside sterilised water 

 was always noted. The culture of the diatom used to inocu- 

 late this medium persists for a considerable period, and the 

 coloui of the frustules remains normal for two to three months. 



(d) Animal-Charcoal Water. — The use of animal 

 charcoal, as a means of purifying the water in small aquaria, 

 has for a long time been known and practised by those who 

 have kept such aquaria in inland places. At an early stage 

 iu our experiments, water from a tank, which was not in 

 a satisfactory condition, was treated with some powdei'ed 

 animal charcoal and filtered. It was noticed that a good 

 growth of diatoms took place in this water. Systematic experi- 

 ments with the use of animal charcoal were then commenced, 

 and these have resulted in a method of great value, both for 

 the culture of diatoms and for the rearing of pelagic larvte. 



Animal charcoal is made by the carbonisation of bones,' 



' Aiitdysis of animal charcoal, from Thorpe's " Dictionaiy of AppUed 

 Chemistry " — 



Carbou . . . . . . lOol 



Ca., Mg. phosphates, Ca. fluoride, etc. . . 80'21 



Calcium carbonate .... 8"30 



Other mineral matter .... 098 



10000 



