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Young rats 23 days of age (Wistar strain) that are offspring of aggressive parents will attack mice. They kill them, however, only if the mother has already killed mice in their presence. Rats 30 days of age will kill mice spontaneously without any previous exposure to killing. The occurrence of muricide activity in young rats of this age is the same as in the adult population. If offspring of aggressive parents are reared by nonaggressive foster mothers from birth, they will not exhibit the muricide reaction at 30 days. In adulthood, however, the reaction appears to the same extent as in the offspring of aggressive parents reared by aggressive mothers. If the descendants of nonaggressive parents are reared by aggressive foster mothers from birth, 64.7% of them will kill mice at the age of 30 days. This aggression is retained in equal intensity during adulthood and cannot be attributed to specific learning in that the mothers have never encountered a mouse in the presence of their foster young.

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a c t i v i t y within t h e renal tissue of Helostoma in general shows good a g r e e m e n t w i t h t h e d i s t r i b u t i o n of this e n z y m e w i t h i n t h e k i d n e y of t h e d o m e s t i c fowl s , this process m u s t no d o u b t be considered of more general importance.B o w m a n s c h e n K a p s e l n gefunden. Die Tubuli waren frei, a b e r der U r e t e r zeigte eine positive R e a k t i o n sowoht ffir Cholinesterase wie a u c h fiir Pseudocholinesterase. The Effect of Early Weaning on Spermioi~enesis in Adult RatsI n f a n t rats can be w e a n e d from the m o t h e r animal and can live i n d e p e n d e n t l y w h e n aged 15-18 d a y s postnatally, while n o r m a l l y t h e y are weaned on a b o u t the 30th p o s t n a t a l d a y L I t was s h o w n in previous p a p e r s t h a t early (premature) w e a n i n g s h o r t e n s t h e lifespan of female r a t s ~, decreases fertility ~ and t h e i r ability to learn (elaborate c o n d i t i o n e d reflexes) w h e n aged 8 m o n t h s is w e a k e n e d 3, a l t h o u g h their final b o d y weight a n d a p p e a rence are unaffected.In order to t h r o w f u r t h e r light on the i m p a i r e d fertility of p r e m a t u r e l y w e a n e d rats, t h e testicles of rats of the W i s t a r B-KonArovice strain were e x a m i n e d in animals w e a n e d n o r m a l l y (day 30) a n d p r e m a t u r e l y (day 18). T h e y were raised on a s t a n d a r d diet*, did n o t come into c o n t a c t w i t h female animals, and were killed b y dec a p i t a t i o n w h e n aged 6 or 12 m o n t h s .I t was found t h a t in 6 m o n t h s old rats the testicles of b o t h groups were n o r m a l (Figure 1 and 2). In animals aged 12 m o n t h s , however, severe degenerative changes are found in t h e p r e m a t u r e l y w e a n e d group, the spermiogenie e p i t h e l i u m being i m p a i r e d or even a b s e n t and s u b s t i t u t e d b y Sertoli cells. Figure 1 shows t h a t the w i d t h of the spermiogenic tubules is also smaller. No i m p a i r m e n t of spermiogenesis was found in n o r m a l l y w e a n e d animals.,°° I Our e x p e r i m e n t s t h u s s h o w t h a t p r e m a t u r e w e a n i n g causes i m p a i r m e n t of spermiogenesis in a d u l t a n i m a l s which c a n n o t be d e m o n s t r a t e d earlier in life (at 6 m o n t h s ) . H o w far this is related to i m p a i r m e n t of fertility in prem a t u r e l y w e a n e d female rats, which had p r e m a t u r e l y w e a n e d males as p a r t n e r s , will h a v e to be elucidated.Zusammen/assung. Junge, vorzeitig (18 Tage nach der G e b u r t e n t w B h n t e R a t t e n ) zeigen im Alter yon 12 M o n a t e n SchAdigungen im s p e r m i o g e n e n H o d e n e p i t h e l . 12 Tage sp/iter e n t w O h n t e R a t t e n e n t w i c k e l n sich normal. Die b e o b a c h t e t e n SchAdigungen t r e t e n im Alter von 6 Mon a t e n noch n i c h t auf.