CHAPTER XX 



RECAPITULATION OF CHAPTERS ON 

 SPECIFICITY 



Examples of Specificity in Nature. — In the three preceding 

 chapters the subject of specificity is discussed rather extensively. 

 It is illustrated by the observations of Loeb and others made dur- 

 ing fertilization experiments, by the physician in skin grafting and 

 blood typing, by the immunologist who is interested in the acute 

 infectious diseases and in biological relationships, by the physiolo- 

 gist in his studies of hormones, enzymes, and various physiological 

 phenomena, by the pharmacologist in liis experiments dealing with 

 the nature and pharmacological action of drugs and by the geneti- 

 cist in his investigation of inheritance. In fact, it is evident that 

 the phenomenon of specificity is a common one in Nature. 



It is important in medicine because all of our serological tests 

 and many therapeutic procedures must be reasonably specific to 

 be of value. 



Antigens. — In earlier chapters attention is called to the fact 

 that the injection of some substances into the animal body may 

 lead to the production of specific antibodies, while the injection of 

 other substances never leads to the production of antibodies. Spe- 

 cific antibody stimulators are called antigens. Their properties are 

 reviewed in these chapters. They are all colloids and aside from 

 a few apparent exceptions, belong to the group of organic com- 

 pounds called proteins. The antigenic properties of various pro- 

 teins are compared with their chemical structure and a number of 

 important facts recorded: 



Properties of Protein Antigens. — 



(a) Proteins are made up of amino acids linked together through 

 their amino and carboxyl groups. They differ from each other 

 according to the number, kind, and arrangement of the amino acid 

 components. Since all proteins give the IMolisch reaction, it is 

 possible that each contains a carbohydrate radical. There is some 

 evidence that globulins contain a lipoid. If carbohydrate or lipoid 

 is present, it will increase the number of possible combinations of 



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