126 



the medium was antimony. The deposit itself was a very inter- 

 esting one, and the interest was increased by the description 

 they had had that evening of what had been found on the slide. 

 Professor Hamilton Smith at that time was experimenting a 

 great deal on media of high refractive index, such as bromide 

 of antimony, bromide of arsenic and piperine, giving an index 

 of a Httle over 2, and they certainly made the objects mounted 

 in them very distinct. There was another thing about this par- 

 ticular culture worth mentioning, and that was, it had never 

 been doctored to any great extent, and therefore the structure 

 stood well in the process of mounting; and the fact of Mr. Nelson 

 finding these tertiary structures was no doubt due to the material 

 not having been over-washed. When mounting in these high 

 refractive media he alw9,ys found this particular culture was 

 much more successfully dealt with than any other. He had not 

 mounted these slides for the sake of the beauty of the specimens, 

 but rather to see the effects of the different media, and it was 

 found almost impossible to mount many of these forms without 

 fracture. 



Mr. Hardy asked if it was possible for a siliceous deposit to 

 become altered after it was once deposited. If it was in a colloid 

 form he could understand that this might be the case, — but 

 supposing it was colloid, would it even then be possible to alter 

 it after it was fixed, because acid did not affect it ? 



Mr. Karop said that it was true that the silica was not affected 

 by acid, but it was very readily acted upon by alkalis. He also 

 asked was this deposit from Nottingham in America ? — because 

 he noticed that Mr. Ingpen referred to it as a "culture," which 

 seemed hardly the correct word. 



Mr. Morland said it was a diatomaceous deposit discovered at 

 Nottingham in Maryland. Later on a fresh find of material 

 from the same locality was called " New Nottingham deposit." 



Mr. E. M. Nelson agreed with Mr. Ingpen that the perfection 

 of the structure in his slide was no doubt due to the fact that 

 the material had not been previously over-cooked. 



Mr. Ingpen thought it highly probable that if the diatoms 

 were cleaned with acid and were not properly washed afterwards 

 some of the mounting media would be affected in the way suggested 

 by Mr. Nelson. 



The President thought that in considering the special forms 



