The Relations between Marine Animai and Vegetable Life. 377 



As will preseutly be shown, the Diimber of bacterial colonies 

 formed from ordinary Aquarium water after 24 hours' incubation is 

 about 1500, aud after 48 hours', about 3000. From this table we 

 see that with waters kept in darkness, the numbers are scarcely 

 ever as high as these, the}^ being generally only a few hundred 

 after 24 hours' incubatiou, and in fìve cases out of eigbteen, less than 

 a hundred. After 48 hours however, the number is more often than 

 not over 1000, and heiice it would seem that the rapidity of multi- 

 plication of the baeteria on gelatin piate culture has been very 

 markedly diminished in addition to the aetual number. With regard 

 to individuai experiments, the first two thìrds of the table consists 

 of observations made with jars of water kept in darkness under 

 similar conditions, but containing respectively ordinary Aquarium 

 water, water filtered through asbestos,, water seeded with other water 

 previously kept in darkness, water placed in a jar covered with a 

 deposit of algfjB, and water previously heated to 100°C. Of these 

 five samples, the seeded water and water in the jar coated with 

 algse coutained the least number of baeteria, and the water heated 

 to 100° the most. The comparatively large number of germs present 

 in this latter water is of interest in connection with the fact that 

 the larvse grown in it were, in contradistinction to those grown in 

 the other specimens of water, considerably smaller than the normal. 

 Determinations made 9 days after these originai cultures showed the 

 numbers of baeteria to be about the same. Those made 24 days 

 later, on the other band, showed a distinct decrease. In the Observation 

 given in this table on a specimen of water kept 74 days in darkness, 

 the number of colonies formed after 24 hours is smaller than usuai, 

 but after 48 hours is just as large. After a further 71 days however, 

 the diminution in number is very conspicuous. Again, in a specimen 

 of water filtered through asbestos, the number of colonies obtained 

 after keeping 65 days is somewhat smaller than after 24 days. 



It may therefore be concluded that the longer a water is kept 

 in darkness, the smaller becomes the number of baeteria it contains, 

 and the slower is their rate of multiplication on piate cultivation. 



On the bacteriology of open sea-water no observations were 

 made, as the subject has already been worked out by Russell • for 

 waters in the Bay of Naples, and very fully by Fischer for Atlantic 

 Ocean waters 2. Russell found the number of baeteria in surface 



1 Zeit. Hyg. 11. Bd. 1891 pag. 165. 

 - ibid. pag. 1—83. 



