AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 91 



some very striking and interesting results have been obtained, 

 but which really give us very little information of value. Molec- 

 ular weights have been assigned as follows : 



Edistin, based on the per cent of sulphur present . . 14,530 



Egg albumin, based on the per cent of sulphur present 15,703 

 Blood serum albumin (horse) based on the per cent of 



sulphur present 14,989 



Blood oxy-haemoglobin (horse) based on the per cent 



of sulphur present ^6,655 



Blood oxy-haemoglobin, based upon iron content . . 15,000 



This discussion so far, though it gives us no clear idea as to 

 the real chemical nature of the proteins, at least shows us very 

 clearly how complex the compounds are and how difficult the 

 study of them is. 



Hydrolytic Decomposition. — Only one line of investigation 

 has resulted in throwing any light on the subject. When pro- 

 teins are boiled with acids or alkalies, hydrolysis takes place by 

 addition of water and the splitting of the complex compounds 

 into simpler compounds. These simpler compounds are the 

 amino-acids which we have just considered. This explains 

 why the study of the proteins is taken up at this point, imme- 

 diately following that of the amino-acids. We have given the 

 formulas for thirteen amino-acids. In addition to these thir- 

 teen, five others are known, making a total of eighteen, all of 

 which have been isolated as products formed by the hydrolytic 

 cleavage of proteins. These different amino-acids are obtained 

 in varying proportions by the hydrolysis of different proteins. 

 This gives a better basis for separating or distinguishing different 

 proteins than can be obtained from a study of physical prop- 

 erties. 



It seems, therefore, that as all proteins yield these amino- 

 acids as cleavage products, some proteins yielding nearly the 

 entire eighteen, the proteins themselves are probably com- 

 posed of these compounds as constituent parts. 



