10 



FIRST LECTURE. 



both cases, at any portion of the outer surface ; the latter is, 

 indeed, similar throughout. 



By means of this vital transformation, our lymphoid cell is 

 able, like an amoeba, to shove itself over whatever it rests 

 on ; and thus, very slowly and sluggishly, it is true, wander 

 about. This may be observed in the pus cell in the cloudy 

 aqueous mentioned. In the magnificently transparent cornea 

 of the normal eye of a frog, the lymphoid cells may be seen 

 to wander through the corneal canals in the most distinct 

 manner, so that they gradually pass over the entire micro- 

 scopic field. 



This has been rather drastically expressed by the words, 

 " the cells devour and march." 



Such amoeboid cells may wander into other cell forms 

 which have come to rest. The surfaces of the body have cell 

 layers which are called epidermis or epithelium. This tis- 

 sue participates actively in the catarrhal irritations of the 

 mucous membranes. Lymphoid cells then wander from the 

 deeper layers of the latter into the bodies of these epithelial 

 cells (Fig. 16). These strange cells had already been ob- 

 served before the vitality of the 

 protoplasma was conjectured. 

 The process was then naturally 

 not understood. It was then 

 imagined that the lymphoid cells 

 were produced within those of 

 the epithelium. 



A form of cell has long been 

 known, a species of epithelium, 

 which presents the most strik- 

 ing vital phenomena. This is 

 the ciliary cell (/). Very small 

 and thin cilia, which cover the 

 free surface of the cell body, 

 are constantly occupied in a 

 to and fro motion. These vibrations are repeated with such 

 extraordinary rapidity that the human eye is unable to dis- 



Fig. 16. — Pus corpuscles in the interior of 

 epithelial cells from the human and rnam- 

 malial body ; a. Simple cylinder cell of the 

 human biliary canal ; b, one with two pus 

 cells ; r, with four, and d, with many of 

 these contained cells ; e, the latter isolated ; 

 f, a ciliated cell from the human respiratory 

 apparatus with one, and g, a flattened epi- 

 thelial cell from the human urinary bladder, 

 with numerous pus corpuscles. 



