164 SENSE OF SMELL. 



been filtered from the wind by the gauze of the vane at the mast-head. 

 Sir Charles Lyell also gave him four packets of dust which fell on a vessel 

 a few hundred miles northward of these islands. Professor Ehrenberg 

 found, that this dust consisted, in great part, of infusoria with silicious 

 shields, and of the silicious tissue of plants. In five little packets 

 which Mr. Darwin sent him, he ascertained no less than sixty-seven 

 different organic forms ! The infusoria, with the exception of two ma- 

 rine species, were all inhabitants of fresh water. 



Mr. Darwin has found no less than fifteen different accounts of dust 

 having fallen on vessels when far out in the Atlantic. From the direc- 

 tion of the wind whenever it has fallen, and from its having always 

 been observed during those months when the harmattan is known to 

 raise clouds of dust high in the atmosphere, it is pretty certain that it 

 must proceed from Africa. It is, however as Mr. Darwin remarks 

 a singular fact, that, although Professor Ehrenberg is acquainted with 

 many species of infusoria peculiar to Africa, he found none of these in 

 the dust sent him; but, on the other hand, discovered in it two species 

 which he knew as living only in South America. " The dust," says 

 Mr. Darwin " falls in such quantity as to dirty everything on board, 

 and to hurt people's eyes; vessels even have run on shore owing to the 

 obscurity of the atmosphere. It has often fallen on ships when seve- 

 ral hundred, and even more than a thousand miles from the coast of 

 Africa, and at points sixteen hundred miles distant in a north and south 

 direction. In some dust, which was collected on a vessel three hundred 

 miles from the land, I was much surprised to find particles of stone 

 above the thousandth of an inch square, mixed with finer matter. After 

 this fact, one need not be surprised at the diffusion of the far lighter 

 and smaller sporules of cryptogamic plants." 



The air is not the only vehicle for odours. It has been seen, that 

 they adhere to solid bodies ; and that, in many cases, they can be 

 separated by aqueous or spirituous distillation. The art of the per- 

 fumer consists in fixing and preserving them in the most agreeable and 

 convenient vehicles. Yet, it was at one time strenuously denied, that 

 they could be conducted through water ; and, as a natural consequence 

 of this, that fishes could smell. M. Dumeril, for example, maintained, 

 that odours, being essentially of a volatile or gaseous nature, cannot 

 exist in fluids ; and, moreover, that fishes have no proper olfactory 

 organ ; that the part which is commonly considered in them to be 

 such is the organ of taste. This opinion is entertained by few. We 

 have seen that odours can be retained in fluids, and not many natural- 

 ists of the present day will be hardy enough to deny that fishes have 

 an organ or sense of smell. At all events, few anglers, who have used 

 the oil of rhodium, or other attractive bait, will be disposed to give up 

 the results of their experience without stronger grounds than any that 

 have been assigned by the advocates of that view of the subject. Be- 

 sides, air is contained in considerable quantity in water, so that odor- 

 ous substances might reach the olfactory organs through it. 



When it was determined, that odours consist in special molecules 

 given off from bodies, it was attempted to explain their action on the 

 pituitary membrane in the same manner as that of savours on the 



