70 PHYSIOLOGY FOR NURSES 



passes in. the blood to the kidneys and is excreted in 

 the urine, constituting; the chief organic substance in 

 the urine under normal conditions. Tissues which wear 

 out and are broken down likewise give rise to the pro- 

 duction of urea, since they are protein material. 



Though under normal conditions, proteins are broken 

 down into amino acids before absorption, nevertheless 

 the tissues possess the power to break down more com- 

 plex protein bodies that may enter the circulation. The 

 occurrence of anaphylaxis (literally "without a guard") 

 or anaphylactic shock is explained in this way. A com- 

 plex protein body is introduced into the circulation, 

 either by subcutaneous or intravenous injection or by 

 passing through an abnormal mucous membrane. Hav- 

 ing entered the circulation, the tissue cells elaborate an 

 enzyme capable of decomposing it into its constituent 

 "building stones." It is assumed that this process is 

 rather slow and gradual; the enzyme is produced in 

 small amounts so that there is no poisoning as a result 

 of the first introduction of the foreign protein. Once 

 the enzyme is produced by the tissue cells, however, it 

 remains active for some time. Now, at some later time, 

 if the same protein is introduced into the circulation, 

 its decomposition starts rapidly, since there is still the 

 necessary enzyme present. As a result of this rapid 

 action, intermediate products of the decomposition are 

 produced in large enough numbers to produce mild, 

 severe, or even fatal poisoning. The urticaria (nettle 

 rash) often seen after injection of diphtheria antitoxin, 

 asthmatic attacks, and similar manifestations are now 

 considered to be instances of anaphylaxis. 



It has already been pointed out that carbohydrate, 

 fat, and protein are required for proper nutrition. Pro- 

 tein is absolutely essential for constructive processes ; 



