ECOi^OMIC IMPOETAKCE OF DIATOMS — MAI'TN'. 379 



earth was mixed with flour, and although the nutritive value of this 

 added substance is practically nothing, the advantage of its use was 

 an actual one; because, when the normal requirement of the human 

 stomach for a " square meal " is a quart, and the available flour for 

 that meal is a half pint, the unfortunate consumer gets at least the 

 semblance of a full dimier by adding to his food supply three times 

 its volume of harmless and inert matter. This is probably the ex- 

 planation of the custom of those tribes known as the " earth eaters." 



A number of years ago and shortly after the invention of nitro- 

 glycerine, the diatoms came into an economic use of great importance, 

 namely, the manufacture of dynamite. This substance, so great 

 a blessing and a curse to mankind, is essentially nothing but nitro- 

 glycerine absorbed into the cavities of dried diatom earth. As each 

 diatom plant is a microscopically small silica box, the walls of which 

 are perforated with intensely minute openings, the diatom earth 

 serA'es to isolate tiny particles of nitroglycerine in such a way as to 

 render the liquid practically a solid and at the same time to obviate 

 the dangerous quality of free nitroglycerine of exploding by means 

 of shock and at low temperatures. To-day, although diatomaceous 

 earth is used to a considerable extent as an element in nitroglycerine 

 explosives, it has been somewhat replaced by other substances, as for 

 example, wood meal. 



If the meaning of the word economic is not too rigidly taken 

 and may include our increased facility in certain lines of research, it 

 is proper to mention among the economic uses of these plants their 

 value in the determination of certain problems of oceanography, 

 especially in the determination of the direction and the extent of 

 the great ocean currents. Those familiar with this phase of research 

 are aware of the great difficulties attendant upon the accurate meas- 

 urement of the extent and speed of an ocean current, due to the fact 

 that the vessel from which such observations have to be made is itself 

 a drifting object, acted upon by the current in question, as well as 

 by the wind and other forces difficult to compute. Could the ship 

 be anchored, this disadvantage would vanish; but inasmuch as this 

 phase of oceanographic research is carried on in the deep seas, 

 anchoring is not practicable. These organisms, on account of their 

 peculiar structure, composition, and size, lend themselves perfectly 

 to studies of this kind. It is perhaps safe to say that they are the 

 only organisms which meet fully the requirements. Being com- 

 posed in part of an indestructible substance, they do not suffer the 

 rapid decay of many of the microscopic organisms of the sea. This 

 is equally true of other marine organisms incased in silica ; but none 

 of these have a second characteristic of the diatoms which is of equal 

 importance, namely, a minuteness of size sufficient to enable them to 

 be carried hundreds or thousands of miles by ocean currents. Such 



