3IO THE PROTOZOA 



a term like "vital phenomena." Unexplained phenomena are daily 

 seen in the laboratory, but the explanations are not regarded as 

 hopeless ; the sudden stoppage of a piece of camphor moving on 

 the surface of pure water, by the introduction of the end of a finger, 

 which gives to the water an exceedingly minute quantity of fatty 

 matter, yet enough to equalize the surface tension, is understood 

 through the laws of physics, although causes cannot be seen. At the 

 present time, we can no more hope to understand the properties 

 which we call "life" than we understand the ultimate causes of surface 

 tension, of aquosity, or universal gravity; yet its manifestations can 

 be examined and measured, and reduced to laws which are already 

 applied in the domain of physical science. 



The Protozoa, finally, must be regarded as forms in which the 

 organism is less developed than in any other animal. In other words, 

 the coordinating factors by means of which each protozoon acts as a 

 unit are less complex than in other representatives of the animal 

 kingdom, and this fact justifies the hope which lies at the bottom 

 of modern "vitalism," that some day we may interpret these unknown 

 factors in chemical and physical terms. 



SPECIAL BIBLIOGRAPHY IX 



Balbiani, G. Recherches experimentales sur la me'rotomie des Infusoires cilies.. 



Recueil zool. Suisse, V., 1888. 



Berthold, G. Studien liber Protoplasmamechanik. Leipzig, 1886. 

 Biitschli, 0. Untersuchungen liber mikroskopische Schaume und das Protoplasma. 



Leipzig, 1892. 

 Greenwood, M. On the Digestive Process in Some Rhizopoda. Jour, of PhysioL 



(English), VII. and VIII., 1886 and 1887. 

 Griffiths. A Method of demonstrating the Presence of Uric Acid in the Contractile 



Vacuoles of Some Lower Organisms. Proc. Roy. Soc. Edinburgh, XVI., 1889. 

 Hofer, B. Expe'rimentelle Untersuchungen liber den Einfluss des Kerns auf das. 



Protoplasma. Jen. Zeit., 1889. 

 Jennings, H. S. Studies on Reactions to Stimuli in Unicellular Organisms. Amer.. 



Jour. Phys., II., 1899. 

 Le Dantec, F. Recherches sur la digestion intra-cellulaire chez les protozoaires. 



Ann. d. rinst. Pasteur, IV., 1890. 

 Meissner, M. Beitrage zur Ernahrungsphysiologie der Protozoen. Z. w. Z.^ 



XLVL, 1888. 

 Rhumbler, L. Physikalische Analyse von Lebenserscheinungen der Zelle. Arch.f. 



Entiuickelungsmechanik, VII., 1898. 



Verworn, M. Psychophysiologische Protistenstudien. Jena, 1889. 

 Id. Die physiologische Bedeutung des Zellkerns. Arch.f. d. Ges. Physiologie, 



LI., 1891. 

 Id. Allgemeine Physiologic. Leipzig, 1894. Translated by F. S. Lee, New 



York, 1899. 



