HUMAN PHYSIOLOGY. 



CHAPTEE I. 



PROTOPLASM AND THE CELL. 



THE tissues of animals, including man, are made up of a substance 

 which is variously termed protoplasm, bioplasm, and sometimes biogen. 

 Protoplasm as found in the bodies of the more highly developed animals 

 is variously changed ("differentiated") to adapt it to many special 

 functions, so that, as may be seen, it is often hard to recognize the typical 

 protoplasm in the many-colored tissues of a man: bone, muscle, epi- 

 thelium, nerve, etc. The bodies of human beings, then, are made of 

 highly differentiated sorts of protoplasm, each developed for some 

 particular purpose in some special way. The functions of each can be 

 understood, however, only when the fundamental general nature of all 

 protoplasm has been learned. It is for this purpose that a chapter will 

 be devoted to the composition, structure, and general functions of 

 protoplasm. 



PROTOPLASMIC STRUCTURE. 



The General Properties and Nature of Protoplasm. As seen with the 

 naked eye, or under a low degree of enlargement, undifferentiated 

 protoplasm appears as a nearly transparent, usually colorless, viscid 

 liquid. It is entirely insoluble in water. It is coagulated and killed by 

 many agencies, e. g., by about 50 C. of heat, by alcohol, strong acids, 

 alkalies, and many other chemical substances; it is disorganized by 

 powerful currents of electricity. Its specific gravity is about 1250; that is, 

 protoplasm is about one-quarter heavier than water. Seen under the 

 microscope, it reflects light nearly as actively as does oil. The most 

 important characteristic of protoplasm physically is its colloidal fluidity, 

 the consistence being such that it will flow freely and yet retain its proper 

 shape, as determined by the sort of cell or animal which it composes. 

 No property is more essential to living matter than this, for movement, 

 the prime external attribute of all life, depends, of course, directly on 

 the mobility of protoplasm, on the freedom of the motion of particle on 

 particle. 



Protoplasm is dependent on heat for its activity, which is greatest at 



