THE NA I'Tll.l S. \'21 



2. The shells in the top cases that are exposed to Ityht are "practically 

 unaffected. 



This points strongly to bacteria. The deadly action of direct 

 sunlight on bacteria is well known, and may produce death in from 

 five minutes to an hour when they are in the vegetative condition. 

 Even strong diffuse daylight suffices to retard or even inhibit the de- 

 velopment of many bacteria. 



3. The shells in the drawers kept in the dark are the worst at- 

 tacked. 



This necessarily follows from the above statement. Darkness is 

 favorable to the development of these fermentative organisms. 

 Within the shell the bacteria would even in the top cases be pro- 

 tected from the inimical effect of light. 



I stated in my former paper that the corrosion had not occurred in 

 private collections. Since its publication I have been informed that 

 some shells in a large private collection at Birmingham have been 

 badly corroded, and have caused anxiety for some time past. 



PREVENTION. 



It must surely be conceded that an infallible remedy cannot be 

 given. My critics have either overlooked or paid no attention to 

 the fact that the corrosion does not appear until after the lapse of 

 about ten years. 



The suggestions received are : 



1 . Boiling in oil. 



2. Rubbino 1 over the surface with such substances as oil of tur- 



D 



pentine oil of cloves, and formalin. 



I am of the opinion that these may be dismissed as ineffectual. 

 Now that we know that the corrosion is caused by bacteria," I am more 

 than ever convinced that soaking in corrosive sublimate solution, 

 combined with previous thorough cleaning, will prove effectual. It 

 must be remembered that corrosive sublimate is an extremely poison- 

 onous substance. The drawers should be thoroughly aerated at in- 

 tervals, to remove accumulated acid vapors, which will never be 

 present in more than minute traces. 



The drawers should also be kept well dried. 



