PROTECTION AGAINST HUNTING 289 



two orders: morphological and physiological. From a morpho- 

 logical and ultrastructural point of view they have the following 

 features in common: basophiha due to free ribosomc granules 

 without much endoplasmic reticulum; sparse, swollen mito- 

 chondria; weak cellular polarity; irregular cellular outlines; high 

 nucleus-cytoplasm ratio; and hypertrophic nucleoh. From a 

 physiological point of view, they are both characterized by: high 

 anabohc activity; rapid rhythm of cell reproduction with 

 numerous mitoses; relatively low degree of differentiation as 

 compared to normal adult tissues; high pinocytotic activity, 

 apparently reflecting similar surface properties ; and, fmally, great 

 plasticity and adaptation power. From these numerous similarities, 

 the possibihty arises that, as far as immunological facihtation is 

 concerned, embryonic tissues may behave somewhat hke tumour 

 tissues. 



All the preceding considerations led us to try to prevent new- 

 born animals from runting by enhancing them in the same w^ay 

 as transplanted tumours are allowed to grow by enhancement. 

 The present work is concerned with passive enhancement of the 

 newborn submitted to injection of homologous adult spleen cells. 

 This, if successful, was thought to have a double interest: 

 theoretical, by showing the possible mechanism by which runting 

 is normally prevented; and practical, by providing a way of 

 preventing runting and eventually obtaining an increased ratio of 

 tolerant animals as compared to the number of treated animals. 



GENERAL DESIGN OF THE EXPERIMENTS 



The general design of the experiments is rather simple : two 

 strains of mice, A and CB A are schematically involved. Antisera 

 against strain-A lyophihzed tissues are prepared in strain-CBA 

 adult mice. Strain-A newborns are injected with strain-CBA 

 adult spleen cells and with CB A anti-A sera in minute, presumably 

 enhancing, doses. 



