PROTECTION AGAINST HUNTING 3O5 



day of age. In order to make comparison between the two series 

 easier, the number of deaths has been expressed in terms of 

 percentage in Fig. 6. The figures of these histograms and some 

 other experimental facts provide information which should be 

 useful to the understanding of the mechanisms both of runting 

 and the protective activity of facilitating sera. The informa- 

 tion concerns the events happening respectively before and after 

 day 7. 



(a) Before day 7. It is generally considered that deaths taking 

 place before day 7 cannot be ascribed to runting because there are 

 other factors which may increase the mortahty during this period. 

 This is true indeed: 18 of our litters (81 newborns) had all been 

 eaten before day 7, whether the newborns had been treated or not. 

 However, among the 75 litters kept for study there had been a 

 different mortality rate according to the series considered: 

 between day o and day 7, 7 out of 83 (8-4 per cent) untreated 

 normal animals died and 13 out of 197 {6-6 per cent) animals 

 treated with homologous cells plus facilitating serum died also. 

 They can be considered (as far as mortahty rate is concerned) as 

 members of the same population of 280 animals of which 20 

 (7- 1 per cent) died between day o and day 7. During the same 

 period 21 out of 170 (i2- 3 per cent) of the animals treated with 

 homologous cells plus normal serum died. It can easily be 

 calculated that, in this last series, roughly 9 animals (that is 43 

 per cent of the deaths and 5 • 3 per cent of the animals) died for a 

 reason which was peculiar to that series — a reason which is inter- 

 preted as early runting. This is in agreement with Russell's (i960) 

 description of runting beginning around day 5. Further signifi- 

 cant information given by studying this early period is the total 

 absence of runting in animals treated with enhancing serum. 



(b) After day 7. The upper histogram of Fig. 6 shows that, in 

 unprotected animals, the maximum mortahty from runting 

 occurs around days 11-12 and that it decreases progressively but 

 has not completely stopped by day 35. The lower histogram of 



