44 ORIGIN OF WHITE CORPUSCLES. [BOOK i. 



In this connection it may be worth while again to call attention 

 to the fact that the corpuscle contains a very large quantity indeed 

 of water, viz. about 90 p.c. Part of this, we do not know how much, 

 probably exists in a more or less definite combination with the 

 protoplasm, somewhat after the manner of, to use what is a mere 

 illustration, the water of crystallization of salts. If we imagine a 

 whole group of different complex salts continually occupied in turn 

 in being crystallized and being decrystallized, the water thus en- 

 gaged by the salts will give us a rough image of the water which 

 passes in and out of the substance of the corpuscle as the result of 

 its metabolic activity. We might call this " water of metabolism." 

 Another part of the water, carrying in this case substances in 

 solution, probably exists in spaces or interstices too small to be seen 

 with even the highest powers of the microscope. Still another 

 part of the water similarly holding substances in solution exists at 

 times in definite spaces visible under the microscope, more or less 

 regularly spherical, and called vacuoles. 



We have dwelt thus at length on the white corpuscle in the 

 first place because as we have already said what takes place in it 

 is in a sense a picture of what takes place in all living structures, 

 and in the second place because the facts which we have mentioned 

 help us to understand how the white corpuscle may carry on in 

 the blood a work of no unimportant kind ; for from what has been 

 said it is obvious that the white corpuscle is continually acting 

 upon and being acted upon by the plasma. 



31. To understand however the work of these white cor- 

 puscles we must learn what is known of their history. 



In successive drops of blood taken at different times from the 

 same individual, the number of colourless corpuscles will be found 

 to vary very much, not only relatively to the red corpuscles, but 

 also absolutely. They must therefore ' come and go.' 



In treating of the lymphatic system we shall have to point out 

 that a very large quantity of fluid called lymph, containing a very 

 considerable number of bodies very similar in their general cha- 

 racters to the white corpuscles of the blood, is being continually 

 poured into the vascular system at the point where the thoracic 

 duct joins the great veins on the left side of the neck, and to 

 a less extent where the other large lymphatics join the venous 

 system on the right side of the neck. These corpuscles of lymph, 

 which, as we have just said, closely resemble, and indeed are with 

 difficulty distinguished from the white corpuscles of the blood, 

 but of which, when they exist outside the vascular system, it 

 will be convenient to speak of as leucocytes, are found along the 

 whole length of the lymphatic system, but are more numerous 

 in the lymphatic vessels after these have passed through the 

 lymphatic glands. These lymphatic glands are partly composed of 

 what is known as adenoid tissue, a special kind of connective 

 tissue arranged as a delicate network. The meshes of this are 



