THE PROTOPLASMA AND THE CELL. 



Fig. 3. — Amoeba ; a, nucleus ; !', vacuoli ; r, alimentary 

 bodies taken in. 



though in the interior of 

 this constantly change- 

 able protoplasma, to- 

 gether with excavations 

 (/>), and small foreign 

 bodies (c), accidentally 

 taken up from the neigh- 

 borhood, a roundish 

 structure with small 

 punctiform contents (a), 



is found. The contained body bears the name of the kernel 

 or nucleus ; the small bodies enclosed within the latter are 

 called nucleoli. The entire creature has the significance of a 

 simple naked cell. What service the nucleus renders the 

 amoeba we are, at present, unable to say. We now leave 

 these lowest creatures, and pass, at a bound, to the highest 

 animal form — to examine the human body. Its parts have 

 been called organs since the primitive days of medicine. They 

 correspond to the separate pieces of one of our machines. It 

 was also long since known that certain substances of our 

 bodies, such as bone, cartilage, muscle, and nerves, were re- 

 peated in all portions of the organism and, slightly or not at 

 all changed, enter into the structure of the most different parts 

 of the body. These substances, which maybe compared to 

 the different materials of which the machine is formed, were 

 early known to be composed of still smaller parts. They were 

 compared to the products of the loom, and designated as 

 tissues. This name has been retained, and that branch of 

 anatomical science which treats of these homogeneous parts, 

 is called the science of tissues, or Histology. 



On attempting, with the aid of the knife and scissors, to 

 separate such tissues, we, at first, succeed very readily ; the 

 fragments permit of a new division, and this may, perhaps, be 

 repeated on those thus obtained. But at last — sometimes 

 sooner, sometimes later— a period arrives when even the finest 

 and sharpest tools become unserviceable ; they are too blunt, 

 too coarse. 



