418 
living substance are always combined to form 
a living system. The simplest living system 
is the cell, which comprises at least three 
structural substances, plasm, nucleus and mem- 
brane. More than one quarter of the text is 
devoted to metabolism. Here the author’s 
tendeney to avoid the conventional, which is 
evident throughout the book, is at once illus- 
trated by his sharp separation between 
“ Baustoftwechsel,” and “ Betriebstoffwech- 
sel,’ comprising respectively the metabolic 
processes involved in the building of body 
substance and those not so involved. The ac- 
tions on metabolism of such conditions as 
temperature, light, altered concentration of 
food stuffs, hunger, absence of oxygen, and! ac- 
cumulated metabolic products are discussed. 
In a subsequent chapter on nutrition, the au- 
thor presents with experimental evidence his 
theory that many aquatic animals are nour- 
ished by organic food dissolved in the sur- 
rounding water, and maintains that this has 
now been proved for many ccelenterates, ento- 
mostracans, tunicates and some fishes. Re- 
sorption is discussed from the modern stand- 
point. The chapter headed “Exchange of 
Matter,” allows a modern treatment of such 
general physiological topics as the resorption 
of oxygen and of solid substances in solution, 
the exchange of water, excretion, secretion, 
and the distribution of matter in plants and 
animals. Here many of the facts and prin- 
ciples of respiration, excretion and circula- 
tion are introduced, but there is no attempt 
to treat these topics along the conventional 
lines of vertebrate physiology. The chapter 
on the conditions of life ends with a discus- 
sion of the problem of the duration of life, 
with references to the work of Calkins and of 
Woodruff. 
A separate chapter is devoted to transforma- 
tions of energy and includes mechanical and 
chemical energy, light, electricity and heat. 
The author accepts Hiirthle’s ideas regarding 
the structure of muscle and, following Kolt- 
zoft’s general conception of the relations of 
plasm and fibrille, believes the fibrillar rods 
to be elastic bodies which are under tension 
when the muscle is at rest. In contraction 
SCIENCE 
[N.S. Von. XXXV. No. 898 
there occurs a sudden change in the osmotic 
relations of the sarcoplasm and the isotropic 
disk, either a decrease of osmotic pressure in 
the former, or an increase in the latter; the 
membrane between the two undergoes an in- 
crease in permeability; water passes from the 
sarcoplasm to the isotropic substance; and 
the elastic tension of the fibrillar rods is re- 
leased. Froéhlich’s view of tonus is followed, 
according to which tonus represents a slight 
tendeney to continuous contraction of a rela- 
tively small number of the fibers of a highly 
irritable muscle, resulting from the action of 
very feeble stimuli coming from nerve tissue. 
Contracture, on the other hand, is a purely 
muscular condition present in fatigued, nar- 
cotized and asphyxiated muscle, and repre- 
sents a partial inability of all the muscle 
fibers to extend their elastic elements. The 
cilium, like the muscle fiber, contains an elas- 
tic and a plasmic constituent, and the inter- 
actions of the two result in the ciliary move- 
ment. Amceboid movement is probably simi- 
lar in principle, the elastic element perhaps 
being represented by the superficial layer of 
the ameboid cell. The increase in the perme- 
ability of the plasmic membrane that occurs 
during contraction is associated with a rever- 
sible coagulation resulting from the action of 
the stimulus on metabolic processes. 
Under the general heading of responses to 
stimuli the author discusses many of the cur- 
rent topics of general physiology, such as irri- 
tability, the law of the threshold of stimula- 
tion, the all-or-nothing law, conduction, the 
latent period, fatigue, the treppe, the refrac- 
tory period, spontaneity, taxis and tropism, 
tonus, rhythm and the question of its myo- 
genic or neurogenic origin, and the relation 
between irritability and metabolism. In 
many of these the author shows himself to be 
under the influence of the school of general 
physiology that is headed by Verworn. Sense 
organs are treated in a broad manner, atten- 
tion being given not only to the various special 
senses of animals, but to analogous mechan- 
isms in plants, such as the ocelli in leaves and 
the static relations of starch grains. In dis- 
cussing the possibility of hearing by fishes a 
