Notices of Books . 191 
The observations on the formation of precipitates in living cells 
recall those made by Darwin 1 on roots and chlorophyll-corpuscles 
on treating them with carbonate of ammonia and other alkaline 
salts. Further, the fact that Schwarz obtained precipitates by means 
of electric shocks, suggests that the ‘ aggregation ’ induced by 
stimulation in the tentacle-cells of Drosera, etc. is to some extent 
a phenomenon of precipitation. 
With regard to the ectoplasm and the * vacuole -membrane/ 
Schwarz concludes that these are membranes of precipitation, and 
that consequently it is impossible to isolate them as distinct struc- 
tures. The thick vacuole-membrane described by De Vries 2 is re- 
garded by Schwarz as an artificial product formed on the death of 
the cell. The microsomata appear to consist of various different 
substances, and not to be structural constituents of the protoplasm. 
The cytoplasm consists chemically, according to the author, except 
in the case of very young cells, of one proteid substance, which he 
terms cytoplastin. 
Throughout the work there are numerous observations as to the 
physics of vacuolation which may be conveniently brought together. 
The author’s theory of vacuolation, which is remarkably simple, is 
based on the fact that vacuolation only takes place in a mass con- 
sisting of at least two substances, one of which is insoluble but capable 
of limited swelling by imbibition, the other being soluble. He proves 
this by showing that no vacuolation takes place in a mass of a pure 
substance, such as gelatin, which is capable of limited imbibition, 
and this overthrows the possible view that vacuolation may be simply 
due to the imbibition of a larger quantity of water than the substance 
can retain in its molecular interstices. On the other hand, it does 
not necessarily follow that, in a mixture of a swelling substance, 
and of a soluble substance, vacuolation will be induced on the 
addition of liquid, as the author shows by examples. A further 
condition is, that the insoluble substance should be impermeable 
to the solution of the soluble substance. This last condition probably 
sets up surface-tensions which lead to the aggregation into drops 
of the solution of the soluble substance. 
The various phenomena of vacuolation presented by chloroplastids, 
1 Journal Linn. Soc., Botany, vol. xix. 1882. 
3 Pringsheim’s Jahrb. f. wiss. Bot. xvi. 1885. 
