116 



SCIENCE. 



[N. S. Vol. XVIII. No. 447 



must have been many hundreds of these ar- 

 rows in one single spheroid. Perhaps an ob- 

 late spheroid is not the best description of 

 one of these masses. They resemble more a 

 long capsule used in pharmacy with rather 

 sharper ends, or the cigar-shaped balloon of 

 an airship. 



In looking for the cause of the discharge I 

 suggested to Mr. Howard that it might be due 

 to the contraction of the cell walls, due either 

 to pressure of the cover glass or to drying. 

 Mr. Howard suggested, and it is a very plaus- 

 ible reason, that it might be osmotic pressure 

 due to the presence of certain mineral sub- 

 stances in the mother liquor. He proposes 

 to test this theory experimentally by making 

 a salt solution for mounting, to imitate, if 

 possible, that within the bomb and thus to 

 exclude osmotic pressure. Presumably, when 

 left in the tissues of the plant the crystals are 

 not discharged; at least, in the preparation 

 which was under observation no free crystals 

 were found until the bomb began to discharge 

 the missiles; as the plant would grow older, 

 however, and the osmotic conditions change, 

 or the cell walls begin to dry, the discharges 

 would begin to take place in the tissues of the 

 plant. These bombs are bundles of crystals 

 and are, of course, exceedingly small, and most 

 of them would doubtless escape rupture dur- 

 ing mastication, but a sufficient amount of 

 them would discharge their arrows to account 

 for the pricking sensations attending the 

 mastication of this material. 



Mr. Safford, who, while connected with the 

 navy, spent some time among the Polsmesians 

 and made a study of the foods in common use, 

 says that this plant is one of the principal 

 food staples of the Polynesians and other 

 Pacific islanders, who eat both the starchy 

 rootstock, either baked or made into paste, and 

 the young leaves which taste not unlike as- 

 paragus. 



If the plant is not thoroughly cooked its 

 acrid qualities remain in some degree. If 

 thoroughly cooked they are destroyed. It is 

 interesting to note that in cases where the 

 leaves are chewed, either fresh or dried, the 

 stinging sensation is not perceived until a 



few moments afterward, and in many cases 

 it is not until the taro root has been eaten 

 that the prickling sensation in the lining of 

 the mouth and throat shows that it has not 

 been thoroughly cooked. 



Alocasia indica, a plant closely allied to the 

 taro plant, is so acrid that the Pacific island- 

 ers resort to it only in cases of great scarcity 

 of food. The disagreeable effects caused by 

 these plants seem to be confined to the tem- 

 porary prickling sensation of the mouth and 

 throat. They are undoubtedly nutritious and 

 are held in high esteem by the natives. The 

 acrid principle in the manioc or cassava is at 

 least partly due to the presence of hydrocyanic 

 acid, and this is removed by cooking. It will 

 be interesting to see if any of this poisonous 

 acid is also found in the taro and Alocasia 

 indica. 



In the case of an Indian turnip lately ex- 

 amined by Mr. Howard, the capsules were 

 found to be somewhat smaller and the crystals 

 larger and shorter than those described. A 

 drop of the sap of the taro, which was shown 

 under the microscope to contain no crystals, 

 did not produce a burning sensation when 

 placed in the mouth. On the contrary, a drop 

 of the juice of the Indian turnip which carried 

 free crystals was quite active in producing 

 the characteristic symptoms. These facts are 

 additional evidence to support the theory at 

 first mentioned. 



While not yet fully established, there is pre- 

 sumptive evidence that the pricking and burn- 

 ing sensation experienced in masticating ma- 

 terials of this kind is mostly of mechanical 



°"S^^- H. W. Wiley. 



THE SEMINAR METHOD IN NATURAL SCIENCES, 

 ESPECIALLY IN ZOOLOGY. 



Any one who has watched, for a number of 

 years, the announcements of the lectures at 

 German universities, will have noticed that 

 the so-called ' Seminar-Uhungen,' ' Colloquia,' 

 or ' Besprechungen,' and ' Wissenschaftlichen 

 Gesellschaften ' have been extended more and 

 more, and now take often an important place 

 among the coui'ses offered by a department. 



The desire of reaching the student better 



