PART I. 



EXPERIMENTAL GENERAL PHYSIOLOGY. 



THIS field of physiology is devoted to the laboratory observation 

 of the general activities of the cells and tissues of living plants and 

 animals. The study of cells is taken up under the head of Cytology. 



CHAPTER I. 

 CYTOLOGY. 



I. ALG^ OR GREEN PLANTS OF LOW ORDER. 



CYTOLOGY is devoted to the systematic treatise of the cell as a 

 living organism, with reference to form as well as to function. In 

 the unicellular organisms it is not profitable to make a sharp division 

 between the discussion of the form and function; they should, rather, 

 be discussed together. 



Interesting objects for the illustration of cell life are the Algse, 

 which are representatives of the lowest sub-kingdom of plants. 

 Some of the Algse are unicellular and some are multicellular. Some 

 are motile and some are non-motile. All are provided with chloro- 

 phyll, which is a coloring matter, usually emerald-green, though 

 sometimes a brownish-green and sometimes a bluish-green. Desmids, 

 Protococcus, and Spirogyra are examples of non-motile Algae possessed 

 of green chlorophyll. 



Desmids. These little plants are composed of a single cell, which 

 may be circular, oblong, or crescentic. Each plant is divided into 

 symmetrical halves, and the margins and the distribution of the 

 chlorophyll are symmetrical and ornamental. 



Protococcus. The green, dust-like coating of the tree-trunks and 

 fence-posts is really composed of myriads of minute green plants, 

 which are composed, like the desmid, of a single cell, though these 

 cells are often loosely held together in colonies or families of three 

 or four a short time after the young are formed. Reproduction in 



