472 Journal of Agricultural Research voi. xiii, no. io 



lowing test was decided upon because of its promising nature. If an 

 antitoxin — for example, tetanus antitoxin — is a substance of nonprotein 

 nature, it should be possible to prepare artificial digestion mixtures con- 

 taining the antitoxic serum or derived globulin in such a manner that the 

 protein would undergo digestion without loss of antitoxin. Appropriate 

 chemical measurements would indicate the extent to which proteolysis 

 has taken place, while inoculation experiments on guinea pigs would 

 indicate whether there was any loss of antitoxic units. If, on the other 

 hand, the antitoxin is a protein, and its power to immunologically neu- 

 tralize the corresponding toxin is a function of the intact protein molecule, 

 then the antitoxin would be destroyed in every case where the proteins 

 had undergone cleavage, regardless of whether the cleavage was caused 

 by a proteolytic enzym or other chemical agent. Due regard must, of 

 course, be had for the possible destruction of the toxin by the chemical 

 agents used. 



However, these theoretical considerations were not the only ores that 

 prompted the present investigation. For practical reasons numerous in- 

 vestigators studied the possibility of immunizing animals by admin- 

 istering the antitoxin by mouth. Some found that tetanus and diphtheria 

 antitoxins were destroyed in the digestive tract; others found that the 

 animals could be so immunized. The present work on the effect of 

 digesting tetanus serum or derived globulin in vitro was expected to 

 throw some light on the fate of immunity units administered per os. 



WORK OF PREVIOUS INVESTIGATORS 



Table I briefly summarizes the conclusions of the more important 

 investigations on this subject. Of the two on tetanus serum by 

 Carriere (4) and McClintock and King (9), it is doubtful whether either 

 led to entirely correct conclusions. McClintock and King state {p. ^02) — 



. . . we are now able to take series after series of guinea-pigs or rabbits, and by 

 the oral administration of [tetanus, diphtheria] antitoxin save 100 per cent of the 

 treated animals, when the antitoxin is administered before the toxin; while the 

 untreated ones, receiving the same dose of poison, invariably die . . . 



In their experiments with diphtheria and tetanus antitoxins {p. J13) 

 administered to men by mouth they demonstrated the presence of the 

 antitoxin in the blood of the men who had swallowed it a few days 

 before the guinea-pig inoculation test. Their numerous positive im- 

 munizations by mouth led them to conclude that — 



. . . the diphtheria or tetanus antitoxin, which had been administered to the 

 individual, had resisted digestion and had been absorbed in sufficient quantities to 

 cause the protective antitoxin to be present in the blood of the individual . . . 



These remarkable results by McClintock and King, although appar- 

 ently obtained under carefully controlled conditions, have not carried 

 conviction with them; they have not served as a starting point for 



