2 53 

 THE CORROSION OF SHELLS IN CABINETS. 



SUPPLEMENT. 



By L. St. G. BYNE, M.Sc. 



(Read before the Society, June 14, 1899.) 



At the time of writing my former paper 1 I did not possess any know- 

 ledge of bacteriology, but I had come to the conclusion some months 

 before that the corrosion was due originally to the action of bacteria. 

 I am now enabled through the kindness of Dr. Ewart to adduce a 

 considerable amount of evidence in support of this. I still adhere to 

 the five items of my previous summary. 



The white powdery substance upon the surface of the shells was 

 found to consist of calcium butyrate, in some instances mixed with 

 calcium acetate. It was formed by the action of butyric and acetic 

 acids upon the calcium carbonate of the shell structure. 



Since butyric acid does not occur in the atmosphere, it can hardly 

 have had an external origin. It must, therefore, have been derived 

 from fermentative processes occurring in the organic material of the 

 shell, or of adhering portions of the molluscan inhabitant. Both 

 aerobic and anaerobic bacteria are known which can cause various 

 carbohydrates to ferment, producing butyric and acetic acids. It is 

 very often the case that a portion of the liver is left attached to the 

 shell, especially to the apex. This might easily undergo butyric fer- 

 mentation, and, moreover, the same might occur with the adhesive 

 substance used to fix the specimen to its card. Both aerobic and 

 anaerobic butyric bacteria exist, but the common forms are anaerobic. 

 Hence we should expect to find the danger of spoiling increased 

 with imperfect aeration in closed or hermetically-sealed cases, in 

 which at the same time there would be no possibility of the acid 

 products escaping. A little moisture is required to start the fer- 

 mentation ; hence, dry cases should escape, and even in damp air 

 the process can only take place with great slowness, for as soon as 

 the products accumulate to a certain extent fermentation ceases until 

 they have been removed. 



There are also certain forms which can cause proteids to ferment 

 with the production of butyric and acetic acids together with bad- 

 smelling gases. In this case, however, the latter would hardly be 

 perceptible. 



That the mischief is of bacterial origin is supported by the follow- 

 ing facts : — 



1. — Butyric acid has been found. 



This could only be produced by the butyric fermentation 

 of carbohydrates, or even proteid substances. Acetic acid is 

 amongst the fermentative products of butyric bacteria, and 



1 Vide antea, p. 172-178. 



