48 BLOOD. 



at present make any very definite statement. We may say that the proteid 

 myosin, or rather the proteid antecedent or antecedents of myosin, enter 

 in some way into its structure, but we are not justified in saying that the 

 living substance consists only of proteid matter in a peculiar condition. 

 And, indeed, the persistency with which some representative of fatty bodies 

 and some representative of carbohydrates always appear in living tissue 

 would, perhaps, rather lead us to suppose that these equally with proteid 

 material were essential to its structure. Again, though the behavior of the 

 nucleus, as contrasted with that of the cell body, leads us to suppose that 

 the living substance of the former is a different kind from that of the latter, 

 we do not know exactly in what the difference consists. The nucleus, as we 

 have seen, contains nuclein which, perhaps, we may regard as a largely 

 modified proteid ; but being a body which is remarkable for its stability, for 

 the difficulty with which it is changed by chemical reagents, cannot be 

 regarded as an integral part of the essentially mobile living substance of 

 the nucleus. 



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

 fact that the corpuscle contains a very large quantity of water, viz., about 

 90 per cent. 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 engaged 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 meta- 

 bolic 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 important 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 corpuscles, 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 colorless 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 characters to the white cor- 

 puscles 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 



