APPENDIX 



from studies on root nodule bacteria of clovers and plant 

 growth stimulants. These beneficial bacterial nodules were found 

 to exert their deforming action on the root hairs by secreting a 

 certain substance. But when Nutman, Thornton and Quastel 

 tested the action of this substance on various plants, they were 

 surprised to find that it prevented germination and growth. 

 Furthermore they found that this toxic effect was selective, being 

 much greater against dicotyledon plants, which include most 

 weeds, than against monocotyledon plants, which include grain 

 crops and grasses. They then tried related compounds and found 

 some which are of great value in agriculture to-day as selective 

 weed-killers.^^ 



(15) Scientists working on the technicalities of food preserva- 

 tion tried prolonging the " life " of chilled meat by replacing 

 the air by carbon dioxide which was known to have an inhibitory 

 effect on the growth of micro-organisms causing spoilage. 

 Carbon dioxide, at the high concentration used, was found to 

 cause an unpleasing discoloration of the meat and the whole 

 idea was abandoned. Some time later, workers in the same 

 laboratory were investigating a method of refrigeration which 

 involved the release of carbon dioxide into the chamber in 

 which the food was stored, and observations were carried out 

 to see whether the gas had any undesirable effect. To their 

 surprise the meat not only remained free from discoloration 

 but even in the relatively low concentrations of carbon dioxide 

 involved it kept in good condition much longer than ordinarily. 

 From this observation was developed the important modem pro- 

 cess of "gas storage" of meat in which 10—12 per cent carbon 

 dioxide is used. At this concentration the gas effectively prolongs 

 the " life " of chilled meat without causing discoloration.^^ 



(16) I was investigating a disease of the genitalia of sheep 

 known as balano-posthitis. It is a very long-lasting disease and 

 was thought to be incurable except by radical surgery. Affected 

 sheep were sent from the country to the laboratory for investiga- 

 tion but to my surprise they all healed spontaneously within a 

 few days of arrival. At first it was thought that typical cases 

 had not been sent, but further investigation showed that the 

 self-imposed fasting of the sheep when placed in a strange 

 environment had cured the disease. Thus it was found that 



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