552 LECTURE XXIII. 



corpuscles heavily laden with particles of iron, which they carry to the 

 nearest lymphatic. Many discoveries show distinctly that the leucocytes 

 endeavor to carry away foreign substances from the body. It may be 

 regarded as positively established that they play an active part during 

 infectious diseases in striving to make the injurious products of the metabo- 

 lism of micro-organisms harmless, although it is going a little too far to 

 assume that the leucocytes alone have this tendency. The leucocytes 

 also serve to disintegrate dead tissue. In this direction, the solution of 

 the masses of fibrin, which fill the bronchi and the finest bronchioles during 

 pneumonia, is very interesting. There is in this case, as we have already 

 indicated at another place, a regular digestive process that comes into 

 play. The fibrin is decomposed into its constituents and these are 

 resorbed. 



We cannot say much concerning the structure of the white blood- 

 corpuscles. They contain, as cells, all those constituents which we usually 

 meet with in cells. There is not much use in mentioning these constituents, 

 for we are not able at present to draw any conclusions from them, or from 

 their union with the other building stones of the protoplasm and nucleus, 

 concerning the participation of this or that substance in the exercise of 

 definite functions. As soon as our investigations reach the cell, the 

 enigma is too great. 



In addition to the leucocytes we find the blood-plates, which we have 

 already mentioned. These are colorless, gummy disks of a round form. 

 They are said to possess all the characteristics of true cells, and to be 

 also capable of active, amoeboid movement. They undoubtedly partici- 

 pate in the clotting of blood. It is, however, still a disputed question as 

 to the point in the entire coagulation process at which their activity 

 begins. 



Let us now return to the composition of the blood itself. We must at 

 once state that the blood, in its natural state, is almost never utilized for 

 quantitative analytical determinations. Almost all of the investigations in 

 this direction have been made with defibrinated blood. In the first place, we 

 are interested to know the relative amounts of blood-corpuscles and serum. 

 This varies with different kinds of animals, and even in different animals 

 of one and the same species. Moreover, the estimation of the number of 

 blood-corpuscles, and the amount of the serum, cannot be made very 

 exactly. It is an indirect determination. We will briefly mention here 

 that method upon which the figures that we shall give below have been 

 based. It is that of Hoppe-Seyler. 1 The blood-corpuscles may be 

 separated from the serum by means of the centrifuge. By repeatedly 

 stirring the blood with an isotonic salt solution, and renewed centri- 



1 Handbuch der physiol. und pathol. chem. Analyse, p. 272 (1883). 



