Report on the Bacteriology uf Water. 



305 



standing side by side with it. The temperature was rather low, 

 15 C., and the observations soon came to an end owing to the close- 

 focussing objective cracking the very thin cover slip. I made many 

 attempts to measure growths for longer periods under this lens, but 

 the failures were so frequent owing to the extremely thin cover slips 

 and hanging drops necessary for so high a power, and the difficulties 

 of illumination, that I had to abandon them. 



The value of each division of the micrometer scale was found to be 

 from 1'20 ft to l'2o /i, but here again I found it hopeless to attain to 

 greater exactitude of measurement. However, the following attempt 

 is at least interesting. 



On comparing the figures with other measurements at the same 

 temperatures, moreover, they agree very well ; so that it may yet be 

 possible to carry out measurements with this power. 



It should be noticed as a point of importance in what follows 

 that these minute variations observed with the highest powers are 

 not traceable (and probably neutralise one another along the filaments) 

 when longer stretches are measured with the lower powers. 



After considerably greater experience with these curves, I am able 

 to sum up the meaning of these experiments more clearly. 



1. They give evidence that the growth of the filament as a whole 

 is intercalary, and due to increase in length and division of all its 

 cells, along the entire course of the filament. 



2. The different rates in the general growth observed are due partly 

 to differences in temperature, partly to differences in age of the 

 portions observed, partly to differences in the food-medium in which 

 the organism is growing, and partly to other causes. 



3. The small variations in rate of growth, especially those traced 

 under high powers, are due partly to small and unrecorded variations 

 in temperature, e.g., cooling of the thin cover-slip when the bell-jar 

 was lifted (as in the experiment on p. 306), and partly to the causes 

 assigned on p. 302, namely, pauses during the intercalation of the 

 new segment walls, and, no doubt, to some extent, to curvatures in the 

 filaments, and want of practice on my part in recording the observa- 

 tions so accurately as I learned to do later on. 



