THE BLOOD. 551 



designated as hemolysis, can be brought about in quite a number of different 

 ways, as, for example, by freezing the blood and then thawing it. Hemo- 

 lysis is also effected by certain bacterial metabolic products, by those of the 

 higher plants, and also those of animals. We shall subsequently take up 

 this process more in detail. 



The constituent of the red corpuscle which has been best studied 

 as regards its functions, is the pigment of blood, hemoglobin, which we 

 have already met with in the discussion of the respiratory exchange. 

 Before discussing its chemical construction, we will consider the above- 

 mentioned, cellular constituent of the blood, the white corpuscles, and 

 briefly take up the composition of the blood as a whole, and its content of 

 individual substances. The white corpuscles are fully endowed cells. 

 They are not uniform, but occur in various shapes and sizes. It is extremely 

 difficult to say much about the sphere of activity of these bodies, also 

 called leucocytes. Their function has never been satisfactorily explained. 

 They have frequently been designated as agents of transportation. It is 

 very probable that they play an important part in this function of metabo- 

 lism, and accomplish the exchange of substance between the cells of 

 different organs. The number of leucocytes can increase extraordinarily 

 under certain conditions. This phenomenon is most strikingly illustrated 

 in cases of infection, in which case the seat of infection is, under normal 

 conditions, surrounded very quickly by a cordon of leucocytes. They 

 are by no means limited to the blood circulation. They can leave this 

 and penetrate into the tissues. The white corpuscles play a quite different 

 part in the blood from that of the red ones. They are not peculiar to the 

 blood, but merely make use of it as a vehicle. They enter and leave it 

 quite at will. They are to be considered as independent entities. This 

 is evident from the fact that they are independent of the nervous sys- 

 tem and can move themselves forward, autonomously like the amoeba3, 

 by sending out pseudopodia. It is possible that the blood contains, 

 besides leucocytes, which are only temporarily present, others which 

 stand in more intimate relations to the blood. We are not at all sure 

 whether we are to regard the white corpuscles as forming a physiological 

 unit, or whether certain of them have special tasks to fulfill. Our experi- 

 ence with pathological processes makes it seem more probable that differ- 

 ent tasks fall to leucocytes of different forms. The large accumulation 

 of leucocytes during intestinal digestion remains absolutely unexplained. 

 It is extremely probable that they in some way take part in the digestive 

 process, being perhaps active in the assimilation of the food. The fact 

 that they are able to take up substances directly, and transport them away, 

 is shown, for example, by observations concerning the absorption of iron. 

 It is not at all difficult, particularly after administration of inorganic 

 iron salts, to find, by testing with ammonium sulphide, many white 



