480 PHYSIOLOGY OP THE DOMESTIC ANIMALS. 



The white corpuscles are much lighter than the red, as is shown by 

 their being found in greatest number near the upper surface of a blood- 

 clot, and by the fact that when horses' blood coagulates the white blood- 

 cells form a distinct layer on the surface of the red corpuscles. 



The white blood-cells possess great adhesiveness, even while in the 

 blood-current. This adhesiveness of the white cells may also be seen 

 in blood drawn from the body. If a drop of blood is covered with a 

 cover-slip and a drop of \ per cent, salt solution passed under the cover 

 by dropping a little of the solution at one side and drawing it through 

 by placing a piece of bibulous paper at the opposite edge, the red blood- 

 cells may be seen by the microscope to rapidly pass from one side of the 

 field to the other, while the white cells remain adherent to the cover-slip. 

 They, therefore, have a tendency to cling to the walls of the blood-vessel 

 in which they may be circulating, and, since the white cells have an almost 

 fluid consistence, they readily pass through the walls of the capillaries 

 into the surrounding tissue. This especially occurs in inflamed tissues, 

 when the slow blood-current and high pressure favors this transudation ; 

 in fact, according to many pathologists, nearly all pus-cells are supposed 

 to originate in such a transudation of the white blood-cells. 



After passing through the walls of the capillaries in normal circum- 

 stances the white blood-cells directly enter the lymph-spaces in which 

 originate the lymphatic vessels, from which they may again enter the 

 blood-current. It does not, however, follow that all lymph-corpuscles 

 which are thrown into the venous current have originally been derived 

 from white blood-cells which have passed from the blood through the 

 walls of the capillaries into the lymph. We have already seen that 

 man}' lymph-cells originate in the lymphatic glands, are developed in 

 the blood into red blood-cells, and as such are again broken down. This 

 change of the white into red blood-cells appears principally to take place 

 in the red marrow of bones and in the spleen. In these organs capillary 

 arterioles do not pass directly into the venous radicals, but into large 

 spaces, or' lacunae, from which, after passing through a sieve-like cellular 

 net-work, the modified blood-cells enter at once into large venous capil- 

 laries. The passage of the blood into these great expansions naturally 

 produces a great slowing of the current, and it is quite conceivable that 

 time will then be given for profound changes in the blood-cells ; part of 

 the protoplasm of the white cells is changed into haemoglobin, the 

 nucleus appears to be extruded and ultimately dissolved in the blood- 

 serum, and a red blood-cell is thus developed. 



The white blood-cells have a very complex chemical composition; 

 various albuminoids enter into their composition, as well as carbo- 

 hydrates, fats, lecithin, cholesterin, phosphates, and calcium, while the 

 cell-nucleus appears to consist mainly of a phosphorized body, nuclein. 



