BLOOD: ITS GENERAL PROPERTIES 89 



ing or immediately following their absorption from the alimentary 

 canal, and that the tissue cells were nourished from this common pro- 

 tein. It is now known that the amino acids are not immediately syn- 

 thetized into blood proteins after their absorption from the digestive 

 system. The blood proteins are radically different from the tissue pro- 

 teins. Substances which retard or accelerate nitrogen metabolism do 

 not alter the relationship existing between the protein bodies of the 

 blood. This fact indicates that the serum proteins have a function quite 

 independent of the nitrogenous metabolism of the body. They un- 

 doubtedly maintain the viscosity of the blood and assist in preserving 

 its neutrality. Attempts to localize the site of formation of the blood 

 proteins have not been successful. There is some evidence that fibrin- 

 ogen is formed for the most part in the tissues of the splanchnic area 

 (liver). It is quite possible that the blood forms its own proteins, just 

 as do other tissues, from the amino acids it contains. 



THE FERMENTS AND ANTIFERMENTS OF THE BLOOD 



The blood plasma contains many of the ferments present in the tissues. 

 The nature of these ferments has been the subject of many investiga- 

 tions in recent years, primarily because it has been found that they are 

 intimately connected with the problems of immunity. 



Among the ferments the following have been demonstrated in the 

 blood: 



Proteases are probably present normally in the human blood serum 

 in small amounts, but they are found in large amounts in the white 

 blood corpuscles. A protein foreign to the body if injected into the 

 blood ordinarily produces no untoward symptoms, but a second injec- 

 tion following the first by some days will produce symptoms of poison- 

 ing known as anaphylaxis. This fact has led to the assumption that 

 the injection of any foreign protein into the blood promptly leads to 

 the appearance therein of specific proteolytic enzymes which will digest 

 the strange protein into its derivatives, which are poisonous. This 

 power of the body to produce specific proteases has been the subject 

 of much research and debate, and Aberhalden proposed a test for preg- 

 nancy, for cancer, and for other conditions in which he made use of this 

 phenomenon. He believes the presence of placenta or tumor tissue to 

 cause the presence of proteins that bring about the production of specific 

 ferments whose duty it is to rid the system of these substances. Other 

 investigators fail to find the specificity in proteolytic action claimed by 

 Abderhalden, and believe that proteolytic ferments which are capable 

 of digesting foreign proteins are absorbed from the alimentary canal 



