482 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



inhibition, when it becomes a very adhesive, gummy substance, to which 

 probably the adhesive properties of the white blood-cells are due. 



Cholesterin is also a constant constituent of normal white blood- 

 cells. It is not known whether the cholesterin is dissolved or suspended 

 in the protoplasm of the white blood-corpuscles. 



In addition to the above substances which are contained in the liv- 

 ing white blood-corpuscles, there exists in breaking up corpuscles the 

 fibrin ferment which originates in the death of the protoplasm. This 

 substance, which possesses the power of converting soluble into insoluble 

 fibrin, may be regarded as a complicated organic body, and possesses, 

 even when in most minute quantity, the power of decomposing the 

 peroxide of hydrogen, probably with the assistance of the elements of 

 water, and of producing the modified forms of fibrinogen. That this fer- 

 ment is set free by the breaking down of the protoplasm of the white 

 cells, and is not contained dissolved in the plasma of the blood, is ren- 

 dered probable by the following experiment : — 



If the mesentery of the guinea-pig be examined under the micro- 

 scope and a crystal of common salt placed near a small blood-vessel, as 

 the salt melts the inner wall of the vessel will be found to be gradually 

 covered with numerous white blood-cells until the lumen of the vessel is 

 finally obstructed by a plug of white blood-cells. At first the margin of 

 each separate cell is distinct, but soon they become indistinct and the 

 vessel is then filled with a mass of fibrin, white thrombus, which exactly 

 resembles the colorless coagulum which forms in clotting blood-plasma. 



Nuclein is the most important constituent of the cell-nucleus. Nu- 

 clein is insoluble in water and dilute acids, but readily soluble in dilute 

 potash solutions ; when treated with hydrochloric acid it is changed 

 into a stiff jelly. Nuclein is completely indifferent to the action of the 

 digestive juices. 



As every increase in the white blood-cells is preceded by a growth 

 of the nucleus, it is possible that the nuclein plays an important role 

 in the life of the white blood-corpuscles. 



In addition to the white and red blood-corpuscles, microscopic ex- 

 amination of the blood will often reveal the presence of granular nucleated 

 bodies, which are described as blood-plates or hfematoblasts. These 

 bodies vary considerably in size, being usually about one-third the size 

 of a red blood-cell, and, like them, biconcave in shape, have about the 

 same specific gravity as the white blood-cells, and possess the power 

 of amoeboid movement. They occur as pale, colorless, oval, round, 

 or lenticular disks, of variable size, .averaging about 3 fJ.. "By Hayem 

 they are supposed to represent an early stage of development of the red 

 blood-corpuscles. They are about forty times as numerous as the 

 leucocytes, and may be recognized in the circulating blood in the mesen- 



