SPECIAL PROPERTIES OF BLOOD SERUM. 2/3 



There has been much speculation as to the part of the blood 

 which gives rise to these various anti bodies. They are solu- 

 ble and may not be separated by filtration, but on dialysis they 

 behave as other substances of very high molecular weight. In 

 many respects they resemble highly active proteolytic ferments 

 or enzymes as the characteristic phenomena are exhibited even 

 in dilutions of the active serum of I : 20,000, and heat and 

 chemical reagents interfere with the active properties much as 

 in the case of the enzymes. But there are apparently some 

 exceptions which have led certain authors to deny their en- 

 zyme-like character. From the sum of the facts observed 

 in the occurrence and action of the anti bodies several writers 

 have been led to think of them as derived from the breaking 

 down of the highly complex polynuclear white corpuscles of 

 the blood. The behavior of these in the " living " condition 

 has been already referred to; in their disintegration it is pos- 

 sible they may give off more and more of the groups on which 

 their activity depends. But there are other possibilities and 

 these will be referred to in the following section. 



ORIGIN AND MODE OF ACTION OF THE ANTI BODIES. EHRLICH'S 



THEORY. 



In the early days of observations on blood serum immunity 

 the doctrine of the phagocytes received considerable attention. 

 \Yith increase of knowledge this theory was seen to be inade- 

 quate to account for accumulating facts, and the assumption 

 of the soluble proteolytic ferments, the alexins, was next to 

 attract attention. These may be formed from the polynuclear 

 leucocytes or more remotely in the organs where these cells 

 may have their origin, in the spleen, for example, and in the 

 marrow of bones. As the name indicates the alexins are pro- 

 tective substances, but the simple assumption of these bodies 

 acting alone, as a chemical reagent would for example, in the 

 annihilation of intruding bacteria was soon seen to be too nar- 

 row to accord with experience. The phenomenon of immu- 

 nity through the alexins or other bodies is a complex one, but 

 19 



