4 PHYSIOLOGICAL CHEMISTRY. 



the real scientific information as to the enzymes of the animal 

 organism, for example, was limited, in the main, to a rather crude 

 understanding of the enzymes intimately connected with the main 

 digestive functions of the organism. We now have occasion to 

 believe that enzymes are doubtless present in every animal cell and 

 are actively associated with all vital phenomena. As a preeminent 

 example of such cellular activity may be cited the liver cell with 

 its reputed complement of 15-20 or more enzymes. 



In text-book discussions of the enzymes it is customary to say 

 that very little is known regarding the chemical characteristics of 

 these substances since no member of the enzyme group has, up to 

 the present time, been prepared in an absolutely pure condition. 

 Apparently, however, from the nature of the facts in the case, it 

 would be much more accurate to say that we absolutely do not knozv 

 whether a specific enzyme has, or has not, been prepared in a pure 

 state. (Some authors, like Arthus, have assumed that enzymes 

 are not chemical individuals, but properties conferred upon bodies.) 

 The enzymes are very difficult to prepare in anything like a con- 

 dition approximating purity, since they are very prone to change 

 their nature during the process by which the investigator is attempt- 

 ing to isolate them. For this reason we have absolutely no proof 

 that the final product obtained is, or is not, in the same state of 

 purity it possessed in the original cell. Some of the enzymes are 

 more or less closely associated with the proteins from the fact that 

 they are both formed in every cell as the result of the cellular acti- 

 vity, both may be removed from solution by " salting-out," both 

 are for the most part non-diffusible and are probably very similar 

 as regards elementary composition. Hence in the preparation of 

 some enzymes it is extremely difficult to make an absolute separation 

 from the protein. 1 Under certain conditions enzymes are readily 

 adsorbed by shredded protein material, such as fibrin, and may 

 successfully resist the most prolonged attempts at washing them 

 free. We may summarize some of the properties of the great 

 body of enzymes as follows : Enzymes are soluble in dilute glycerol, 

 sodium chloride solution, dilute alcohol and water, and precipitable 

 by ammonium sulphate and strong alcohol. Their presence may 

 be proven from the nature of the end-products of their action and 

 not through the agency of any chemical test. They are colloidal 

 and non-diffusible, and occur closely associated with protein material 

 with which they possess many properties in common. Each enzyme 



1 Others seem to be like the substrate on which they act, e. g., carbohydrate. 



