1002 
cable to the existing case without any manner 
of doubt. The mystery of the great ice age, 
and of the former rich vegetation in the present 
cold zone, still remains to be solved. 
FRANK WALDO. 
An Outline of the Theory of Solutions, and Its Re- 
sults, for Chemists and Electricians. By J, 
Livineston R. MorGan, Px.D. (Leipzig), 
Instructor in Quantitative Analysis, Poly- 
technic Institute, Brooklyn. New York, John 
Wiley & Sons; London, Chapman & Hall. 
1897. Pp. 63. 
The contents of this work are four lectures, 
delivered before the Brooklyn Institute of 
Arts and Sciences, and deal with the theory 
of solutions, methods for the determination of 
electrolytic dissociation, the theory of the 
voltaic cell, and analytical chemistry from the 
standpoint of electrolytic disociation. 
The author states in his preface that ‘‘a 
knowledge of the theory of solution and its re- 
sults, is so important to workers in all branches 
of chemistry and electricity, that the following 
pages have been compiled, containing an ele- 
mentary treatment of the subject.”? * * * ‘If 
by this sketch the author can induce any one 
to go deeper into the subject he will feel more 
than repaid for his work.”’ 
H. C. J. 
Untersuchungen tiber das Erfrieren der Pflanzen. 
Mouiscu. Jena, Gustav Fischer. 1897. Pp. 
viii+ 73. 11 illustrations. 
A notable addition to the physiology of the 
cell has been recently published by Professor 
Molisch as a result of several years’ work upon 
the effect of cold upon plants. 
The researches upon which generalizations 
rest are fragmentary and necessarily inaccurate, 
since they were carried on in the open air or 
under conditions of great discomfort to the ob- 
server. At the same time no regulation of the 
temperature could be effected. Dr. Molisch 
has been enabled to obtain results of great im- 
portance, both from the advance in cell physics 
since the time of Muller’s experiments and by 
the use of ingeniously constructed apparatus. 
Dr. Molisch’s researches were chiefly con- 
ducted by means of a double-walled freezing 
chamber of wood 33 x 33 x 27 em. outside meas- 
SCIENCE. 
[N. S. Vou. VI. No. 157. 
urements. The space of 7 ecm. between the 
double walls on five sides of the chamber was 
filled with sawdust. The center of the chamber 
was occupied by a zine compartment to contain 
a microscope. A tubulated opening through 
the walls of the zine and wooden compartments 
allowed access of light to the mirror, and toothed 
rods for adjustment of the stage, objectives and 
mirror extended outside the walls. The space 
surrounding the zinc compartment was filled 
with a mixture of salt and ice, by which tem- 
peratures of 4°C. to 10°C. were obtained in a 
room kept at 10°C. 
As a useful preliminary, observations were 
made upon the freezing of colloidal substances, 
emulsions, color and: salt solutions. The erys- 
tals were seen to appear suddenly in a colloid, 
such as gelatine, and toincrease in size, extract- 
ing the water from the gelatine, so that the latter 
shrunk into a network resembling parenchyma. 
tissue. Some colloids return to the original 
condition upon thawing; others do not. Starch 
paste is an example of the latter. The sus- 
pended particles in an emulsion, such as latex, 
aggregate in the form of a network of bands 
upon freezing. Freezing of color and salt solu- 
tions result in the more or less complete sepa- 
ration of the solid and solvent. 
The chief interest of the paper lies in the re- 
sults of the direct and continuous observation 
of the freezing of living cells. 
An ameeba, after exposure of 25 minutes to a 
temperature of 9°C., exhibited the formation of 
clumps of ice crystals in the plasma, and finally 
became a solid lump consisting of a complicated 
network of plasma almost devoid of water, ice 
crystals, vacuoles of concentrated cell-sap and 
air-bubbles. Theslender filaments of Phycomy- 
ces froze only when the temperature fell to —17° 
C. The small diameter of the cells seem to be a. 
direct adaptation against freezing. Yeast cells 
exhibited a shrinkage of 10 per cent., due to 
loss of water when the medium was frozen, but 
the cells were not killed at-15°C. The freezing: 
of Spirogyra filaments at —3 to -6°C. isaccompa- 
nied by a shrinkage in diameter amounting to. 
62 per cent. and by the final aggregation of 
chlorophyll band and nucleus in the center of 
the cells. The excretion of water in this plant 
under low temperatures may be easily observed 
