THE BIOCOLLOIDS 131 



Chemistry in general, and physiological chemistry in particular, 

 aims to investigate the structure of individual chemical substances, 

 and thus explain their properties by splitting them, synthesizing "" 

 them, and comparing the regenerated (rearticulated) substance with 

 the original, to see if it is the same or different. Unfortunately, so 

 far as the colloidal constituents of the organism are concerned, they 

 are still far from their goal, especially in the case of carbohydrates 

 and proteins. Here colloid chemistry enters and attempts to com- 

 prehend and where possible to regulate the behavior of the finished 

 product. Colloid chemistry is not occupied with the parts of the 

 machine, but with the machine itself. The chemist splits the pro- 

 teins into polypeptids, amino-acids, etc., but the student of biocolloids 

 avoids such profound attacks and strives to keep the molecule in- 

 tact so far as possible, studying its outward form, the chemical 

 points of attack offered by the unmutilated molecule, its behavior to 

 changes which may occur under normal and pathological conditions, 

 as well as those brought about by drugs. 



I wish here to emphasize one other point. Only a few substances 

 occur in the organism that are suitable for study by the physiological 

 chemist. Serum albumin and globulin, the starches and some of the 

 fats, are unquestionably substances which may be separated from the 

 organism without losing some of their essential properties, but they 

 are exceptions. The substances usually studied by physiological 

 chemists are those which have already suffered considerable modi- 

 fication. The organism possesses neither glue, histone nor myosin, 

 and even if we knew the exact chemical constitution of glue, this 

 would throw no light upon the properties and the function of cartilage 

 and the fibrils of connective tissue from which it is derived. But 

 even without knowing the chemical composition of glue, I believe 

 that it would be possible, with the methods of colloid chemistry alone, 

 to collect a series of observations which would afford valuable con- 

 clusions concerning the chemical mechanisms of such tissues. 



A time will come when the old physiological chemistry and the 

 new chemistry of the biocolloids will meet and the two opposite 

 ends of the tunnel shall be united. We shall first try to learn the 

 properties of the intact colloid molecule of the colloid particle. 

 The following chapters on carbohydrates, lipoids and proteins should 

 be read, bearing this statement in mind. 



