76 MANUAL OF HISTOLOGY. 



recognise also, that certain thin, thread-like processes, consisting of a clear 

 structureless substance, extend themselves rapidly from the main mass 

 (a), while others much broader (b df) commence an extensive ramifica- 

 tion (g li k). Should the branches of neighbouring processes come into 

 contact with one another, they coalesce at the point of contact, forming 

 net-like figures or broad flat meshes, which gradually assume the 

 dark appearance of the rest of the body of the cell. Other prolongations 

 of the protoplasm, on the contrary, have in the meanwhile receded and 

 disappeared in the body of the cell. At times the most extraordinary 

 intermediate forms of the cell result from these changes (?' e). All this 

 time a slow circulation of the granules lying in the protoplasm may be 

 observed, the nucleus moving about passively with them. It is only 

 on the death of the cell that this extraordinary movement ceases, and 

 that the former assumes the round shape (/), formerly supposed to be the 

 only one in which the pus-corpuscle ever appeared. 



The species of cell just mentioned, our " Jymphoid cell" (p. 72), is found 

 widely distributed throughout the bodies of vertebrate animals, and has 

 received different names, according to the region in which it is met with, 

 as, for instance, the " white blood-corpuscle," the " lymph and chyle 

 corpuscle," the " mucous corpuscle," &c.. 



Does it undergo the same changes of form in the human and mam- 

 malian body generally 1 



This question may be answered in the affirmative ; but, owing to the 

 much smaller size of the cell in the latter, and the rapid cooling of the 



preparation, the demonstration of vital 

 contractility is attended with more diffi- 

 culty. The series of changes sketched 

 in fig. 67 may be followed (a, 1-10) on 

 the white corpuscles of the blood; but 

 the energy of the movement is greatly 

 increased if the natural warmth of the 

 fluid be kept up artificially. 



Another instance of change of figure 

 is depicted in fig. 68, which represents 

 a small portion of living connective 

 Fig. e? .-white contractile corpuscles of tissue from the body of the frog. The 



human blood, a, 1-10, changes of shape ce ll s known as COimective-tlSSUe COr- 

 succeeding one another in a cell, within a , , / n i i i 



period of forty minutes' duration; b, & puscles put torth here Very long and 



stellate ceil. thin fiiif orm processes (a b c), but the 



sequence of change is of the slowest kind. These processes meeting 

 together with others like them from neighbouring cells, fuse into one 

 another temporarily. But all such connective-tissue corpuscles do not 

 appear to possess the same power of motion, for at d and e the form 

 is not altered. The stellate cells of corneal tissue are said, however, 

 to afford a much more beautiful example of vital change of form. 



The appearance and disappearance of these protoplasm processes, and 

 their irregular development, resemble in the most striking manner those 

 wondrous variations in figure observed to take place in the body of one 

 of the naked rhizopods, the amceba, which consists entirely of protoplasm ; 

 and we may, therefore, with perfect propriety, adopt the name " amoeboid 

 motion" for the phenomena under consideration. 



It is very easy to convince one's self, with the aid of the microscope, 

 that the amoeba is able to take up solid particles into its body from the 



