410 COLLECTED STUDIES IN IMMUNITY. 



II. 



One of the main causes which has made an insight into the rela- 

 tion between constitution and action so difficult to obtain is to be 

 found in the fact that these relations were considered to be much 

 simpler than they really are, and in the further fact that purely 

 chemical conceptions were applied arbitrarily to biological processes. 

 In pure chemistry there is an abundance of material for observing 

 the relations between physical properties and chemical constitu- 

 tion. In such a study it is first necessary to determine which proper- 

 ties, to follow Ostwald's terminology, are " additive" and which 

 "constitutive " by nature. 



The question arises what are the essential properties which are 

 ;still found in the combinations. Evidently they are such as per- 

 tain to the substance of the elements and are independent of the 

 arrangement of these. These properties accompany the elements in 

 their combinations, assuming therein values which represent the sum 

 of the values of the elements. In other words these are "additive" 

 properties. 



Real additive properties are not known apart from mass. The 

 neaiest approach to them are perhaps the specific heat of solid com- 

 binations, and in a less degree the refraction of organic substances and 

 their property to occupy space. In these, however, another factor 

 becomes evident, namely, the arrangement of the elements in their 

 combinations. This factor is of paramount importance in deter- 

 mining such properties as color, boiling- and melting-point, form of 

 crystals, etc. The properties which are under the mutual control 

 of the nature of the elements and their arrangement are called 

 "constitutive " properties. The extreme in this direction is made 

 up of those properties which are no longer in any way dependent 

 on the nature of the substances but only on their arrangement ; 

 these are called " colligative " properties. 



To which group, then, do the properties of affinity, i.e., the power 

 of elements to effect chemical reactions, belong? Evidently to the 

 constitutive, for daily experience teaches us that the nature as well 

 as the arrangement of the elements is a factor. Acetic acid, lactic 

 acid, and glucose contain the same elements in the same propor- 

 tions by weight, yet they manifest entirely different reacting capaci- 

 ties. Butyric acid and acetic ester are not only of the same con- 



