308 GUY A. VOISIN AND RADSLAV KINSKY 



day 15; they triple it on day 26 and they quadruple it on 

 day 34. As for the two series of animals injected at birth with 

 homologous cells, they have weight curves very close to each 

 other and ascending more slowly than that of the normal 

 controls: the mean weights of day 7 have increased twofold 

 on day 20 and threefold on day 30; they have not increased 

 fourfold by day 35. The weight curve of the protected ani- 

 mals is slightly but consistently above the weight curve of the 

 unprotected animals. A statistical analysis of the coefficient of 

 variation of the mean weights in the 21 experimental situations 

 (21 experimental points on Fig. 7) leads to the conclusion that the 

 differences between the three series on a given day are not signifi- 

 cant (Table II). This can be easily understood from the great 

 variability in weight of individual litters. This great variability 

 depends on two main factors: the number of newborn animals in 

 one litter and the period of the year (the experiments presented 

 here were carried out over two years). However, if one considers 

 each individual litter one can make the following relevant 

 observations: on days 10, 14, 21, 28, and 35, in 88 per cent (+ 3 per 

 cent) of the htters, the untreated normal control animals had a 

 mean weight superior to the mean weight of the experimental 

 animals, while the reverse situation occurred in only 6 per cent 

 (±1*5 per cent) of the litters (the remaining 6 per cent pertains 

 to the Htters where the mean weights were about the same). 

 These figures are, indeed, highly significant. On the other hand, 

 on day 7, in 53 per cent of the litters the control animals weighed 

 more than the experimental ones, while the reverse situation 

 occurred in 7 per cent of the Htters : this is highly suggestive of a 

 true difference. 



Concerning the much smaller difference between the mean 

 weights of the two experimental series (the protected and the 

 unprotected), it has been found that, on each individual day 

 (7, 10, 14, 21, 28 and 35), the protected animals had a mean weight 

 superior to the mean weight of the unprotected animals in 72 per 



