20 MEMORIAS DE LA SOCIEDAD CIENTIFICA 
according to their solubility, density, and so forth. Concentric forma- 
tions, incrustations, etc. 
The study of these internal currents is, one may say, the chief aim 
of physiology. They may be explained in terms of known physico- 
chemical causes rather than by an undiscovered and undiscoverable 
vital force. The causes are— 
A. Diffusion and osmotic currents. 
B. Heat. Oxidations. 
C. Ingestion of the materials that support the phenomena of diffu- 
sion and oxidation. 
D. -Partial vacua and changes of every kind in internal pressure, 
induced by evaporation, etc. 
The action of these causes may be tested by both the natural and 
the synthetic protoplasm. 
A. The use of gummy water is indispensable ¡if one wishes to ob- 
serve the circulation of protoplasm in the elements of trees, and thé 
movements are generally dependent on the conditions of diffusion 
(cf. Biitschli's foams).* The currents of the artificial product vary in 
accordance with the diffusive power of the substances, the quantity of 
liquid, and the presence of some large granulations. 
B. The rapidity of diffusion increases, within certain limits, with 
an elevation of temperature (Graham). The movements of the proto- 
plasm increase in rapidity between 10 and 22 degrees, becoming 
slower beyond those limits, and stopping between 45 and 48 degrees. 
I have seen that at a suitably high temperature these currents pre- 
sent themselves even in very viscous liquids. It is evident that oxygen 
as well as the liberation of heat attendant on respiration are equally 
necessary to every being. 
C. The paralysis of artificial currents ceases completely with an ad- 
dition of peptone or a new quantity of salts. * 
- D. This is an evident principle. It is enough to remember the facts 
concerning the circulation of sap and blood. The paralysis of internal 
A See Milne-Edwards, “Anatomie et physiologie comparte,” tome Y. p, 105, 
