572 L. R. CRAWSHAY. 



as to necessitate partial screening from the light. The intense 

 growth obtained in one-third Miquel water occurred in experiments 

 either with 3 Calanus per litre, or with from 2 to 5 Calanus per 2 litres. 

 During the transition, which was a gradual one, from one-fourth Miquel 

 to pure " outside " water, a thick growth was still obtained in an experi- 

 ment with 1 Calanus in 2 litres, when it was estimated that a trace only 

 of Miquel remained in the water. 



The exact bearing which these facts may have on the problems of 

 Diatom growth which are under investigation by Dr. Allen* will, it is 

 hoped, become more apparent as the experiments are continued. That 

 the action of the Calanus excreta is such as greatly to intensify the 

 growth in the presence of the Miquel salts, even when the latter are 

 used in much reduced proportions, there seems to be no doubt. Whether 

 it is quite an independent one is at present somewhat uncertain, f 



The Influence of some Bacteria on the Experiments, and their Destruction. 



In order to ascertain the possible influence of some of the common 

 Bacteria as contributing to the unsuccessful results of the earlier ex- 

 periments, some special experiments were carried out in which Bacteria 

 w^ere encouraged to grow in large numbers in the water. As a food 

 basis a stock solution of peptone, of 5 grams per litre in strength, was 

 prepared in diluted Berkefeld water, and this was used in very small 

 quantities. 



In some peptone-agar cultures which Mr. Drew kindly made for 

 me, from some infected water, two forms of Bacteria were obtained : one 

 producing large spreading, roughly circular, white colonies, from 1 to 

 5 millimetres in diameter ; the other forming small compact, often 

 almond-shaped, yellowish- white colonies, usually about half a millimetre 

 in greatest measurement. 



Three 1-litre flasks of diluted Berkefeld water were infected with both 

 of these forms, peptone being added in the percentages of -001, -002, 

 and -01, severally. On the following day the water in all the flasks 

 was clouded with Bacteria. 



In the first of these experiments (-001% solution) the cloudiness con- 

 tinued unchanged on the 58th day. On the 68th day, it had nearly dis- 

 appeared, and the peptone being then renewed in the same proportions, 

 the bacterial growth was restored, and continued on the 90th day subse- 

 quently. 



* Cf. Joimi. Mar. Biol. Assoc, N.S., Vol. VIIL, p. 421 ; Vol. X., p. 417. 

 t The most recent experiments support the view that the action is an independent 

 one. — L. R. C, 



