478 Mr. A. J. Walton. On the Variation in the 



were due to such errors they would be less likely to occur in both groups. 

 The ages of the young animals varied from two clays to two weeks, and 

 during this limited period there seemed to be little, if any, variation in 

 the nature of the tissues and plasmata as regards the capacity for growth. 

 One -experiment will be described in detail, the others being carried out 

 on precisely the same lines. 



Experiment 2. — An adult rabbit over a year old was anaesthetised. The fur 

 on the ventral surface of the body was removed, the skin sterilised, the 

 carotid artery laid bare, and the blood collected in sterile paraffined tubes 

 kept in ice. This auimal was kept anaesthetised. Blood was collected from 

 .a young animal five days old and also placed in iced paraffined tubes. Its 

 thyroid and a piece of liver were removed and placed in sterile Einger's fluid. 

 The young animal was killed. Similar tissues were removed from the old 

 animal. The blood was centrifugalised. Cultures of the young animal were 

 made in both plasmata, as were also those of the old animal, six cultures 

 being made in each group. 



The nature of the growth was observed and at certain periods specimens 

 were fixed and stained. After 48 hours the thyroid of the young animal 

 showed marked growth in the old plasma, but that of the old auimal in 

 the old plasma, although showing considerable growth both of the con- 

 nective and parenchymatous types of cell, was definitely less than that of 

 the young animal. On the other hand, both specimens in the young 

 plasma showed either no growth at all or only a few cells growing from 

 the edge of the tissue. Similar results were obtained in the case of the liver. 



The above results are well shown by the following Table : — 





Old plasma. 



Young plasma. 



Young tissue ... 



Moderate growth 

 Very good growth 



Very slight growth. 

 Slight growth. 



The above experiment was performed again 10 times. The old animals 

 were in all cases fully developed, and the majority were known to be over 

 one year of age. The young animals varied in age between two days and 

 two weeks. The cultures were made in groups of four or six in each media 

 and were prepared under identical conditions. By taking groups of four or 

 six specimens it was possible to estimate more accurately the changes in 

 growth, for in the primary cultures it is unusual, excepting perhaps in the 

 case of the testicle, to find that all the specimens have grown to an identical 

 extent. Moreover, the percentage of successful growths in a series is in 



