SO-CALLED 'BIOLOGICAL PROPERTIES' OF MILK 121 



also used mice which were immune to ricin. After the birth of 

 the young, one of the mothers which had been immunised was 

 allowed to suckle young mice from a normal mother, and another 

 immunised mother was allowed to suckle her own young. 

 Immunity to ricin was found in the young of both series and in 

 an approximately equal degree, thus showing that the immunity 

 had been transferred by suckling. 



Experiments on these lines demonstrate the fundamental 

 fact of the transference of immune properties from the mother 

 to the young animal by means of the milk. This fact carries 

 with it the necessity for the absorption of the immune properties 

 by the young animal, and as has already been pointed out, it is 

 necessary for such absorption to be carried out without prior 

 digestion of the protein substances to which the immune properties 

 are attached. 



Two considerations arise consequent upon this fact : (i) The 

 length of time for which such absorption can last after birth, and 

 (2) the amount of immune substances thus absorbed. This second 

 consideration will evidently depend upon the amount of such immune 

 substance present in the milk. The majority of the observations 

 upon these matters have been carried out with antitoxins of one 

 kind or another. The length of time after birth during which 

 absorption can take place directly, varies in different animals, but 

 would not appear to be longer than a few days under normal 

 circumstances. 



Romer (i) worked with diphtheria antitoxin, which he injected 

 into a pregnant mare shortly before parturition. After parturition 

 antitoxin could be detected in the milk in a strength of about 

 ^ of that in the mother's blood. At the time of birth no anti- 

 toxin could be detected in the blood of the foal, but after birth it 

 appeared, and the amount continued to rise until about the twelfth 

 day, after which the content of antitoxin in the foal's blood 

 gradually sank. Later injections of antitoxin into the mother 

 produced a corresponding rise in the antitoxin content of the milk, 

 but did not prevent the continued fall of antitoxin content in the 

 foal's blood. Evidently this experiment implies that absorption 

 of antitoxin took place during the first few days after birth, but 

 that although there may be a higher antitoxin content in the milk 

 at a later date, no such absorption occurs. 



Confirmatory results were also obtained by Hamburger (2) , who 

 found that if a kid twelve days old was fed by a mother who had 

 been injected with tetanus antitoxin very little absorption took 

 place. Working with Sperk and using the precipitin method for 

 the detection of protein, Hamburger failed to obtain evidence of 

 absorption of protein in a calf of three days old, or in infants of from 

 five weeks to thirteen weeks old, to whom horse serum was given. 

 Evidently the children were above the age at which such absorption 

 would be likely to occur, and the work is somewhat complicated 



