1895. NOTES AND COMMENTS. 239 



As regards the tsetse fly, smearing the animals with a mixture of 

 kerosene oil and cow-dung is suggested as a most effectual preventive. 

 The West Indian jigger, a burrowing flea, has also just reached the 

 districts round Lake Nyasa and the Upper Shire, having slowly 

 migrated eastwards from the West Coast, where it was introduced 

 with ballast from Bahia in 1873. 



The Ascent of Sap. 



Why does sap overcome the attraction of the earth and rise to 

 the summit of high trees ? One explanation is that the root-hairs, by 

 the vital action of their protoplasm, as well as by simple osmosis, 

 absorb water from the soil and force it upwards through the stem. 

 It has been shown that when the upper part of a vigorously growing 

 plant is cut off and replaced by a tube containing mercury, the sap 

 continues to ascend with force enough to raise the column of mercury. 

 But even in the absence of "root-pressure" ascending currents are 

 maintained : a shoot out from a stem will continue to absorb water 

 and force it upwards. In a recent communication to the Royal 

 Society (published July, 1895), ^^^- Henry H. Dixon and Dr. Joly 

 support the view that the ' suction-force ' of the leaf is the " all- 

 sufficient cause of the elevation of the sap, not, however, by estab- 

 lishing differences of gas-pressure, but by exerting a simple tensile 

 stress on the liquid in the conduits." Meniscuses are formed in the 

 exceedingly minute membranous mesh work of the evaporating cell- 

 walls, and these are capable of supporting a tension equivalent to many 

 atmospheres pressure, while the columns of liquid in the conduits of 

 the plant supply the loss by evaporation. They support their simple 

 mechanical view by ingenious experiment and inference ; but they 

 admit that the results maybe complicated by osmotic processes in the 

 leaf. We should add that they certainly are complicated by the vital 

 action of the protoplasm. We know now that the protoplasm in all 

 the cells of a plant forms a continuous net-work only incompletely 

 divided by the cell-walls ; and we should hesitate to accept any theory 

 which did not allow for the direct ' vital ' action of this net-work of 

 protoplasm. 



A Polemic from Victoria Park. 



We have received from Messrs. Swan Sonnenschein & Co. a 

 copy of a pamphlet entitled " Microbes and Disease Germs, the Truth 

 about the Anti-Toxin Treatment of Diphtheria," by Edward Berdoe. 

 The question of anti-toxins is of surpassing interest both from the 

 general scientific point of view and from the clinical point of view. 

 As a scientific review we are prepared to give the most careful 

 attention to any serious scientific treatise, and we are ready to make 

 large allowance for rhetorical violence in the treatment of a burning 

 topic. But there must be some evidence that ability to take a serious 



