60 MOISTURE AND PROTOPLASM [Ch. II 



to 15%, when placed under conditions of temperature favor- 

 able to metabolism, show almost no change in the course of 

 days. This has been indicated also by an experiment of 

 KocHs' ('90, p. 685), who placed seeds, which had been dried 

 in a vacuum, in a receptacle connected with a Geissler's tube, 

 such as is used in the spectroscopic study of gases. The air 

 was completely pumped out of both vessels, and after some 

 months a spectroscopic study of the gases iu the Geisslek's 

 tube showed no trace of nitrogen or carbon, yet the seeds later 

 germinated. This experiment can hardly be considered to 

 demonstrate KocHs' point, however, since the seeds were 

 deprived of oxygen, as well as moisture. 



The act of drying may, on the contrary, induce the manu- 

 facture and elimination of certain secretions. This occurs 

 apparently in many Protista, which form cj'sts in the drying 

 pools. This phenomenon is seen again in some of the higher 

 animals, — such as our garden slugs, — which secrete slime in 

 large amount when kept for a short time in a dry place. In 

 both cases the result is of immense importance for the con- 

 tinued life of the organism, — in both cases it is to be consid- 

 ered a response to the stimulus afforded by evaporation of water. 



2. Effect of Dryness upon the Motion of Protoplasm. — We 

 have seen that water plays an important role in the movement 

 of protoplasm. When by any means the water is partly with- 

 drawn, the protoplasmic currents will be slowed. When, on 

 the contrary, protoplasm, which is l}''ing in an " indifferent " 

 medium, such as blood serum, is placed in distilled water, 

 unusually active movements occur. This has been shown by 

 Engelmann ('68, p. 446) in the case of the spermatozoa of the 

 frog, and the ciliated epithelium of the frog's oesophagus just 

 removed from its body. Similarly, Dehxecke ('81) found that 

 protoplasm of the tissue cells of the higher plants exhibited 

 abnormally rapid movements upon adding water. These obser- 

 vations indicate that water may act as a stimulus to the move- 

 ment of protoplasm. 



3. Desiccation-rigor and Death. — It is a familiar fact which 

 has been established by over a hundred and fifty years of 

 experimentation, that some organisms, when gradually dried, 

 may cease from movements. This immotile condition has 



