1905.] Effects of Alkalies, etc., on Eggs of Echinus. 135 



causes at first an increase in rate of growth and division, but as the amount 

 is increased, there appears a marked tendency to irregularity in size and 

 shape of the resulting cells. Nuclear division becomes in advance of 

 cytoplasmic division, so that the cells become multi-nucleated. As the alkali 

 is further increased, both cell division and nuclear division are stopped. 



3. Accompaning the increased stimulus to nuclear division given by the 

 dilute alkali, there are seen many of the atypical forms of mitosis described 

 in malignant growths. The variations from the normal illustrated in the 

 drawings are : (1) multiple nuclei in the same cell in active division ; 

 (2) multipolar mitosis, occurring both in the single cell stage, and later 

 in the development of the organism ; (3) asymmetrical mitosis, leading to 

 unequal distribution of chromosomes to the two daughter cells ; (4) reduc- 

 tion in length of the chromosomes as the strength of alkali is increased until 

 the chromosomes appear as rounded dots, and accompanying the reduction in 

 length there is also a reduction in number to about one-half the normal ; 

 (5) in certain cases the chromatin becomes arranged in circles, each of which 

 shows a number of thickenings. The circles are arranged in groups in the 

 cell, and appear to represent a stage in the anaphase, the groups being placed 

 at about the usual distance apart of the centrosomes, and traces of the 

 achromatic fibres being occasionally visible. 



4. No such increased growth or stimulus to nuclear division is given by 

 varying the normal reaction of the medium in the opposite direction, by the 

 addition of equal small amounts of acid. From the beginning the minutest 

 amount of added acid has an inhibitory effect upon growth and nuclear 

 division. There is no nuclear proliferation as the amount of acid is increased, 

 and at a very slight amount of increased acidity all attempt at cell-division 

 ceases. In the fixed and nuclear stained preparations cell-division figures 

 are absent, and in the resting nuclei the staining power of the chromatin is 

 decreased, so that the nuclei present a washed-out appearance contrasted with 

 the normal nuclei or those of organisms grown in dilute alkaline solution. 



5. The extreme limits at which life and cell-division are possible lie close 

 together, indicating that the cell is very sensitive to even slight changes in 

 the concentration of hydrogen and hydroxyl ion concentration. Thus the 

 addition of so little as - 0015 M. of either alkali or acid to sea-water 

 practically stops all growth. On account of the presence of phosphates and 

 carbonates in the sea-water the change in hydrogen and hydroxyl ions 

 caused by such additions cannot be large. 



{Note added October 24. — Since the paper was written we have had an 

 opportunity through the kindness of Messrs. J. E. S. Moore and C. E Walker 



L 2 



