728 GLOSSARY. 



animals whose temperature varies with that of the surrounding me- 

 dium ; " cold-blooded animals." 



Presbyopia. A term denoting the loss of power of accommodation 

 for near vision, which accompanies old age. 



Protista. A term used to denote the large group of organisms which 

 remain in the primitive state of a single cell during all their lifetime. 



Protococcus. A unicellular vegetable organism, the protoplasm of 

 which contains chlorophyll. 



Protoplasm. The substance which gives rise to the primitive vital 

 phenomena, seen in unicellular organisms, and which is the chief 

 agent in executing the functions of all the active tissues. 



Proto vertebrae. The primitive segments of the mesoblast in the site 

 of the future vertebral column. 



Protozoa. The division of the protista which has been assigned to the 

 animal kingdom. 



Proximal. A term used to denote a part relatively nearer to the 

 centre. 



Pseudopodia. A term applied to the projections thrown out by mov- 

 ing protoplasm, by means of which cells, such as amoebaB, move. 



Ptyalin. The ferment of the saliva. In a weak alkaline solution it 

 converts starch into dextrin and sugar. 



Reflex action. The activity caused by a ganglion cell reflecting an 

 afferent impulse along an efferent nerve to the neighborhood of origi- 

 nal stimulation. 



Refraction. The bending which rays of light undergo when passing 

 obliquely from one medium to another of different density. 



Reticulum. A network; a term applied to the interlacement of fibres, 

 such as is seen in reticulated connective tissue, etc. 



Rheoscopie frog. An arrangement by which the change in the elec- 

 tric current of one muscle of a frog is made to act as a stimulus to 

 the nerve of another. 



Saponiflcation. The formation of soap ; the decomposition of oils or 

 fats by means of alkalies into salts of the fatty acid and glycerin. 



Sarcolactic acid. The principal acid in dead muscle. It has a dex- 

 tro-rotatory power on polarized light, which ordinary lactic acid does 

 not possess. 



Sarcolemma. The delicate sheath surrounding the fibres of skeletal 

 muscles. 



Sclerotic. The fibrous coat of the eyeball. 



Sensorium. That part of the nerve centres which is supposed to per- 

 ceive sensory impressions. 



