492 



Journal of Agricultural Research 



Vol. XIII, No. 10 



The following observations on the results of experiment 2 1 (Table VI) 

 are true of the other experiments in which pepsin was used. 



Mixture a. — This contained only antitoxin 420 F' and was used as a 

 standard with which the other mixtures were compared. 



Mixture b. — This contained the antitoxin in 0.2 per cent hydrochloric- 

 acid solution. From the data in Tables III, VI, and VII it is apparent 

 that the acid destroyed all or very nearly all of the antitoxin in four days, 

 during which time the proteins underwent practically no change. There 

 was a slightly smaller amount of coagulable protein in mixture B than 

 in mixture A, but in the other two B mixtures (experiments 20, 22) the 



dififerences were insig- 

 nificant. The figures 

 for amino nitrogen 

 likewise indicate that 

 while over 87 per cent 

 of the antitoxin was 

 destroyed, the changes 

 in the proteins, as 

 measured chemically, 

 were so slight as to 

 justify the conclusion 

 that under these par- 

 ticular experimental 

 conditions the destruc- 

 tion of the antitoxin 

 involves no protein 

 breakdown. The de- 

 struction of over 96 

 per cent of 

 antitoxin in 





tetanus 

 mixture 



/ 2 3 ^ S 



Fig. 3. — The destruction of tetanus antitoxin ( X ) by 0.2 per _ . 



cent hydrochloric acid without any significant change in the amounts B, experiment 22, Wlth- 



of total coagulable protein ( O ) or free amino nitrogen ^^^ anv significant 



( 1 ). Mixture B, experiment 22. 



change in the amounts 

 of total coagulable protein or amino nitrogen are graphically represented 

 in figure 3. This efi'ect was not recorded by any of the previous investi- 

 gators mentioned on page 473; it probably was not looked for. This 

 affords a second method of separating tetanus antitoxin from associated 

 protein; but the antitoxin is destroyed, leaving the antitoxin-free pro- 

 teins intact. 



Mixture c. — There were no changes in this mixture containing 

 antitoxm and pepsin — that is, there was neither antitoxin destruction 

 nor protein digestion. The lower figures for total coagulable protein, as 

 compared with mixture A, do not indicate a slight proteolysis, but rather 

 a difficulty of obtaining a complete precipitation of the protein in the 



