388 



H. M. Vernon 



Water without alga 



241iours 481iours 



Water with alga 



24 hours 



4Slioiira 



Normal water 



Normal water -|- larvse 



after 8 days' growth . 



Normal water 



Normal water 



Normal water + larvse 

 after 4 days' growth . 



Normal water + larvae 

 after 8 days' growth . 



510 



1040 

 3340 



liquefled 



7160 



+ 15 sq. cm. Viva per 1. 



for 4 days 



•-|- 6 sq. cm. Ulva per I. 



during development . 

 + .6 gm. Gelidium per i. 



for 4 days 



1870 lifiuefled 

 1550 



liquefled 



22000 



800 



2450 

 650 



850 



23000 

 1670 



Water kept 23 days in 

 diffuse light .... 



Same water + larv« 

 after 4 days' growth . 



Same water + larvae 

 after 8 daj's' growth . 



145 



9600 



109U 



870 



20900 



1640 



Thus in each of the three instances given, iu which some alga 

 was added to the water alone, or to the water containing developing 

 larvse, the number of bacteria was iucreased. The next three determ- 

 inations show the effect of keeping water in diifuse light, whereby 

 a layer of diatoms was formed on the sides of the vessel. The 

 number of germs appeared to be practicall}^ the same as in the 

 normal water, and to increase to about the same extent when larvse 

 were introduced. 



It may have been noticed that in all the above results the 

 number of bacteria in the water was invariably larger after two or 

 four days' larvai development than after eight days', or than in the 

 water itself before the addition of the fertilised ova. The numbers 

 present after eight days are mueh more Constant than those found 

 at any other period, but they are generally somewhat larger than 

 those in the original samples of water. Thus of the twenty countings 

 made after eight days' larvai development, in twelve cases the number 

 of germs after 24 hours' incubation varied between 1000 and 2000, 

 and in only three cases did it rise above 2000. These results are 

 in agreement with those of Bolton, Gramer, Fränkel and others^, 

 who found that as a rule, owing to the sudden change of tempera- 

 ture and other conditions, the number of bacteria in a specimen of 

 water taken from a river er other source increases very largely for 

 the first few days, and then decreases again. 



Untersuchung des Wassers, pag. 481 — 490. 



