TISSUES OF THE BODY 223 



The average distance of the corneal corpuscles from one another is 

 0-0226-0-0452 mm. 



After the customary treatment of the cornea with dilute acetic acid, 

 we may recognise in these nodal points nuclei of O'0090-O'Ollo mm. 

 in size (fig. 216, c). And in that, as a rule, the substance of the body 

 of the cell reaches as far as the limiting lines of the space, we have 

 the appearance of a stellate cell clothed with a membrane. The use 

 also of a dilute solution of nitrate of silver for obtaining the like views 

 has been recommended (Recklinghaiisen). 



But we are obliged to turn to the cornea in a condition as far as 

 possible unchanged, in order to gain a correct view of the state of 

 things. Here we see the tissue studded with membraneless stellate 

 cells extending their processes in all directions, and frequently forming 

 a cellular network through union of the latter. This network, in our 

 opinion, lies within the system of canals already mentioned. Very 

 elegant objects illustrating the nature of this cellular network may be 

 prepared with chloride of gold. 



The contractile lymphoid wandering cells of connective-tissue parts 

 (already mentioned, p. 77), were discovered several years ago by 

 Recklingliausen in the cornea of frogs and mammalia also, travelling, 

 as he supposed, through the passages of this structure. This discovery, 

 confirmed on all sides, has led to a multitude of other observations 

 and experiments, which have unveiled most interesting features in cell- 

 life of the widest significance. If we place the excised cornea of one 

 frog in the lymph-sac of another, we may demonstrate this immigration 

 of lymph corpuscles into the corneal tissue (Recklinghatisen). We have 

 already considered the power these cells possess of taking up molecules 

 of colouring matter into their protoplasm. This may easily be brought 

 about by injecting granules of pigmentary substances either into the 

 circulation or into a lymph-sac in a frog. The same injection produces 

 similar occurrences among mammals. Fed in this way, the lymph cor- 

 puscles leaving the blood pass into the corneal tissue, in small numbers 

 indeed, into that which is healthy, but in great quantities, on the other 

 hand, in a cornea which has been inflamed through an irritant (Cohn- 

 heim). But all of these cells, which now go by the name of pus cor- 

 puscles, have not the same source, i.e., from the circulation. There 

 must be a new formation in the interior of the corneal tissue itself 

 (Hoffmann and Hecklinghausen, Norris and Strieker), about which, how- 

 ever, we have but insufficient information at present. 



We will add but one word more on the structure of the cornea at an 

 early period of life. 



In the embryo (fig. 216, rt), the so-called corneal corpuscles show but 

 few processes, and the nuclei enclosed in them appear vesicular. Divi- 

 sion may also be observed among them. The network formed of these 

 is extremely dense as it is first seen (b), and the intermediate substance, 

 originally very scanty, increases in proportion later .on. It is still com- 

 pletely homogeneous and without any cleavage. Double refraction is 

 also absent. The formation of the two transparent limiting membranes 

 also takes place very early. 



REMARKS. The literature to which investigations of the cornea have given rise 

 is very extensive, and frequently very contradictory in its statements. Among the 

 newer works we may mention, beside those of the Germans, Toynbee, Philosophical 

 Transactions for the year 1841, Part 2, p. 179; W. Bcwman, Lectures on the Parts 



