PART II. 

 SECTION I. 



Protoplasm. 



I. Nature of Protoplasmic Activity. 



The first step in the study of physiology must be to 

 acquire as clear and definite a conception as possible of the 

 nature of protoplasmic activity in its most simple and 

 uncomplicated form, for in this way an idea of the essential 

 and non-essential characteristics of life may best be gamed. 



The common yeast (Saccharomyces Cerevisias) aftbrds 

 such a simple form of living matter. 



This plant consists of very minute oval or spherical bodies 

 frequently connected to form chains, each composed of a 

 harder outer covering or capsule, and of a softer inner 

 substance which has all the characters of protoplasm. 



1. Manifestations of Life. — Its vital manifestations may 

 be studied by placing a few torula? in a solution, containing 

 glucose, CgHioOg, some nitrogen- containing substances such 

 as urea, CONgH^, or ammonium nitrate, NH^NOg, with 

 traces of disodium phosphate, Na2lIP04, and of potassium 

 sulphate, K2SO4 (Practical Physiology). 



If the vessel be kept all night in a warm place, the 



clear solution will in the morning be seen to be turbid, and 



probably covered with froth. An examination of a drop of 



the fluid shows that the turbidity is due to the presence of 



myriads of torulse. In a few hours the few torulse placed in 



the fluid have increased many hundredfold. The whole 



mass of yeast has grown in amount by the growth and 



multiplication of the individual units. 



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