PROTECTION AGAINST RUNTING 



303 



tective effect. It seems, therefore, that below a threshold dose, 

 enhancing sera have no striking activity. 



(c) Number of injections. The influence of this factor was 

 studied with serum AN-BII: 57 animals received only i injection 

 (o'20 or 0-25 mm.^) at birth; 52 animals received a similar 



8> 



70 

 60 

 50. 

 40 i 

 30 

 20 

 10 

 

 10 

 .201 



ANIMALS TREATED WITH : 



Homologous cells ♦ normal serum 



Homologous cells + serum 



"'AN-BI or AN-B*T 



_ Nothing ^... 



(normal controls) 



I) 



Birth' and 

 injections 



TT 



28 35 



Days after birth 



Fig. 4. Cumulative curves of mortality (same method as in Fig. i). 

 Protected animals have been treated with sera AN-BIII or AN-B+T, 

 two sera of high activity ; protection is both relative (delayed occurrence 

 of runting) and absolute (great decrease in the fmal proportion of deaths). 

 Number of animals ahve on day 7: 40 protected; 33 unprotected; 18 

 normal controls. 



injection at birth, followed, between day 5 and day 17, by one to 

 three further injections (0-20 to 1-50 mm.^), the dose being 

 increased with the age of the animals. Eighty-eight animals 

 received normal serum at birth and some of them received 

 additional injections of normal serum. Finally, 40 animals received 



