634 
sealed again without introducing any foreign 
substance, gave such a large percentage of 
fatalities that too large a percentage of fatali- 
ties in the experiments proper should not be 
attributed to the reagent. 
Magnesium Chloride—The magnesium 
chloride was employed as a 10 per cent., 16 
per cent. and 83 per cent. dilution of the 
molecular solution of the salt in normal salt 
solution; that is to say, ten parts of the 
molecular solution of magnesium chloride 
were diluted with ninety parts of normal salt 
solution; ete. 
The reagent was introduced into the eggs 
in the same manner as was the chlorotone; in 
some eases into fresh eggs, in other cases into 
the eges after they had been in the incubator 
from ten to twenty hours. 
The effect of these weak magnesium chlo- 
ride solutions was about the: same as the 
chlorotone, the embryos being killed in prac- 
tically every case, or, at least, the process of 
incubation was inhibited. As in the case of 
chlorotone the results were here largely vi- 
tiated by faulty technic in opening and 
closing the eggs for the introduction of the 
reagent. 
These preliminary experiments, as has been 
said, while too limited in number to give 
definite results, will serve as a guide for fur- 
ther work, especially in regard to the char- 
acter and strength of reagents and the length 
of time they should be allowed to act. 
ALBERT M. REESE 
WEST VIRGINIA UNIVERSITY 
INHIBITION OF CELL DIVISION IN PARAM@CIUM 
In connection with the discussion of “ po- 
tential immortality” in Protozoa (in other 
words, their ability to continue their physical 
existence indefinitely, barring accident and 
disease, through the bodily “splitting up” of 
each individual into its two offspring, each 
repeating the process, which is continued “ ad 
infinitum”) it may be of some interest to 
note the length of time an individual has 
been observed to maintain its identity—in 
other words, to continue living, without divid- 
ing into its progeny. The writer has suc- 
SCIENCE 
[N.S. Vou. XXXV. No. 903 
ceeded in preventing one specimen of 
Paramecium caudatum from dividing, for 
the space of a little over thirty-two days, by 
keeping it confined in capillary tubes of bores 
too small to permit it to turn back readily. 
Control specimens had meanwhile divided 
on an average of once a day. In other words, 
if the confined specimen had been allowed to 
divide unmolested, it would have divided into 
four billion, two hundred and ninety-four 
million, nine hundred and sixty-seven thou- 
sand, two hundred and ninety-six offspring! 
The irritation caused by the confining walls 
is doubtless a factor of as great importance as 
the accumulation of the products of excretion, 
and the lack of nutrition; since specimens 
which were daily taken from their tubes and 
allowed to swim about in a fresh infusion con- 
taining an abundance of Bacterium termo, for 
a number of hours before being transferred to 
new tubes, nevertheless refused to divide. 
Particles which appear to be cast-off por- 
tions of the specimen’s body, were frequently 
observed in the tubes with individuals thus 
treated, thus suggesting that increase of 
protoplasmic bulk may take place without the 
customary sequence of cell division, even in 
well-nourished individuals. 
Conklin’s observations on Crepidula seem 
to indicate that the dwarfing of those forms 
in small hermit crab shells (dwarf forms being 
always found in small hermit shells, and 
“eiant” forms in large hermit shells) is due 
to an inhibition of cell division, since the 
difference in size is due to the difference in 
the number of cells, rather than to differences 
in cell size. Crustacea, Echinodermata, Mol- 
lusea, Amphibia, ete., reared in small vessels 
are always dwarfed, and this too must be due 
to an inhibition of cell division. 
In the case of Crepidula, the fact that the 
hermit shells are open to the ocean would indi- 
eate that the accumulation of waste products, 
and lack of proper nutrition can hardly be re- 
garded as a sole, or even the chief, cause of 
this inhibition of cell division, and the writer 
is inclined to the opinion that narrower con- 
finement in some way acts as an important 
factor in the process. 
