PKOTOZOA 19 



and it is evident also that precipitated protoplasm is not the 

 same as living protoplasm. But bacteriological methods, 

 experiments with drugs, and haemolytic and other reactions 

 have demonstrated that it is specific and even individual in 

 peculiarity. 



The condition of the water in which the cell lives, with 

 respect to salinity, density, temperature, and viscosity, deter- 

 mines the volume and the shape of the cell and the intensity 

 of the physiological processes. The volume tends to increase 

 in fresh water and to contract with increased salinity, and 

 this is associated with osmotic pressure. These conditions 

 have also an influence on the rate of action, and even the 

 presence of the contractile vacuole. The shape of the cell 

 may be altered with change in temperature and the associated 

 change in viscosity. The accumulation of products of decom- 

 position acts detrimentally on some Protozoa and encourages 

 others. Thus Biochemistry and Biophysics have arisen as 

 sciences of importance which are rendering welcome help to 

 the morphologist, the physiologist, and even the psychologist. 



Physiology. Multiplication is periodic, and after each 

 event the cell starts from half size and grows to full size. It 

 is clear then that the food material, some of it, is converted 

 into living protoplasm. In all the Protozoa which we have 

 examined the food may be observed in the process of being 

 ingested and the undigested remains egested. The endo- 

 plasm provides vacuoles in which it undergoes changes. The 

 food as such disappears, and we feel from what we observe 

 with regard to growth that it is being digested and dissolved 

 in the process. It follows that the contact of the food with 

 the endoplasm provokes the secretion of enzymes or ferments 

 capable of killing, breaking up and dissolving the food. It 

 has been demonstrated, in fact, that the first enzymotic 

 action is accomplished in an acid state, and the subsequent 

 ones in an alkaline state. The digestion then is quite similar 

 to that which takes place on a larger scale in the higher 

 animals. In the case of the cell, digestion and absorption are 

 necessarily intracellular. The enzymotic fluids secreted by 

 the protoplasm first reduce the food to a simple, soluble con- 

 dition, and then reassemble it to suit the constitution of the 



