288 



INTRODUCTION 



[Ch. X 



are summarized in the curve, Fig. 79. This shows how the 

 growth in length of the bacterial rods is delayed at intervals 



; SECOND PERIOD OF MINMrGROWTH,S 

 WHEN 2D CELL DIVISION 

 A WMiil FIRST CELL DIVISION OCCURRED. 



PERIOD OF MINM. GROVH'H, 



Fig. 79. — Curve of growth of a bit of a filament of Bacillus ramosus, 27.30 y- long at 

 the beginning and 70.88 h at the end of the period of observation. The curve 

 shows certain periods of diminished growth (indicated by the arrows below the 

 curve), which correspond to cell-division. From Wakd ('95, p. 300). 



by the nuclear divisions and the accompanying formation of 



transverse septa.* 



The course of , 

 normal growth may 

 now be studied in 



* Attention may here 

 be called to aphenomenon 

 which has repeatedly 

 been observed when a. 

 single growing mammal 

 has been weighed at 

 regular intervals. This is 

 a sort of alternation of 

 periods of unusually rapid 

 growth with periods of 

 diminished growth, the 

 Interval being a day or 

 two. There is an irregu- 

 larity in the length of 

 these periods. See Saint- 

 Loup, '9.3 ; compare also 

 MiNOT, '91, Table XIV. 



Fig. 80. — Curve of length of shell of Lymnsea atagnalis 

 at intervals from hatching up to 85 days. From 

 Sempee, Animal Life, p. 163. 



