328 



EPITHELIAL AND ENDOTHELIAL TISSUE. 



Aside from some special secretions, there are three varieties 

 viz. : the watery, the mucous, and the fatty. (See Fig. 142.) 



(a) The watery secretion cannot be directly studied under the 

 microscope. We may infer, by watching amoeba? laden with car- 

 mine particles, that, at the time when, through the visible con- 

 traction of the living matter within the body, carmine particles 

 are thrown out from the interior of the amoeba, a certain amount 

 of its fluid is discharged with them. We come to this conclusion 

 from the fact that the carmine granules are extruded with a 

 certain force, in a stream of liquid. We must also conclude that 

 the opening in the wall of the amoeba kindly and immediately 

 closes, for the amoeba displays the same amount of activity after 



FIG. 142. DIAGRAM OF THE PROCESS OF SECRETION. 



The series W illustrates the watery secretion: a, a plastid, with foreign granules in the 

 meshesof the reticulum ; b, escape of some granules, with some bioplasson liquid. 



The series M illustrates the mucous secretion : a, mucous globule formed at the top of the 

 epithelium ; b, a mucous globule discharged ; c, a mucous corpuscle discharged ; in both latter 

 cases a goblet left. 



The series F illustrates \\\& fatty secretion : a, first-formed fat-granules ; b, coalescence of 

 fat-granules into a fat-globule. 



as before this process. A liquid present in the blood, which is 

 to be excreted, must necessarily pass through the walls of the 

 blood-vessels and first enter the epithelia before it can be expelled 

 from them. The discharge of a certain amount of liquid 



