78 SOLUTIONS AND PROTOPLASM [Ch. Ill 



strength, however, varying for different individuals (Engbl- 

 MAiSTN, Czbrny), death rapidly ensues. Thus Amoeba quickly 

 breaks up in a 10% solution, and the ciliated epithelium of a 

 frog's throat in a 2.5% solution. Four phases in the action of 

 concentrations may thus be observed : stimulation, retardation, 

 density-rigor, and death. Even in concentrations at which 

 motion is not entirely inhibited, locomotion may be interfered 

 with. Thus, RiCHTBE ('92, pp. 37-40) found that while normal 

 Tetraspora swarm-spores move at the rate of about QOfi per 

 second, or else rotate about 100 times per minute, those in an 

 11% solution hardly move from their place, or sometimes 

 move one-eleventh as fast as the normal swarm-spores. While 

 it is possible that the dense water affords a mechanical obstacle 

 to locomotion, it seems more probable that it is the general 

 diminution of activities which causes the slow migration. 



The modification of excretion by abnormal concentrations 

 has been studied especially by Rossbach ('72). This experi- 

 menter worked upon fresh-water Ciliata (which alone possess a 

 contractile vacuole) by subjecting them to a 0.5% solution of 

 NaCl. The contractile vacuole became diminished almost to 

 invisibility, and the interval between contractions was in- 

 creased. In a 1% solution of sugar a reduction in size of the 

 contractile vacuole occurred, but this was not so marked as in 

 the case of the 1% NaCl solution. This is what we should 

 expect according to theory, for the number of molecules in a 

 1% solution of sugar (mol. wt., 342) is much less than in a 1% 

 solution of NaCl (mol. wt., 58.5), and their relative osmotic 



2 3 



action is as — — : — --, or as 0.002 : 0.017, or as 2 : 17. 



8 X 342 3 X 58.5 



The phenomenon of contracting vacuoles seems not to be 

 confined to Protozoa. It occurs in the embryos of some Mol- 

 lusca, especially the stages of fresh-water Pulmonates, upon 

 which my friend. Dr. Kqfoid, performed some density experi- 

 ments. The early cleavage and blastula stages of many fresh- 

 water Pulmonates contain a central fluid-filled vacuole, which 



300 atmospheres loses its contractility, and at 400 atmospheres becomes rigid 

 and hard. It also increases immensely in weight by the addition of water. 

 EoGER pointed out that, subjected for 2 minutes to a pressure of 3000 kilograms 

 per sq. cm., certain bacteria (Streptococcus) are even killed. 



