NON-MATHEMATICAL SCIENCES 179 



their capacity for reproduction, but it has been 

 pointed out that in a minor way crystals have 

 the power of reproduction. If into this beaker 

 (containing a supersaturated solution of so- 

 dium thiosulfate) I drop a minute crystal, it 

 grows. I take a bit of this new growth and inocu- 

 late a second beaker, and so I may go on. Some 

 years ago in our laboratory we wished to deter- 

 mine some properties of crystallized glycerine. 

 We tried in every known way to make glyc- 

 erine crystallize, but in vain. However, we dis- 

 covered that some crystallized glycerine was in 

 storage at a certain place in British Columbia, 

 and importing a sample of this, the laboratory 

 at once became "infected" by glycerine crystals, 

 and no matter what new sample of glycerine 

 was used there never was any difficulty in mak- 

 ing it crystallize. 



There is a peculiar phenomenon known as tin 

 disease or the tin pest. In cold climates organ 

 pipes, roofs, and other objects made of tin often 

 disintegrate and fall into dust, and a sort of 

 quarantine has to be established to prevent the 

 disease spreading as an epidemic from those 

 pieces of tin which have once become infected. 

 Yet this all proves to be due to the fact that 

 the gray, powdered tin is a more stable form at 



