294 NATURAL SCIENCE [May 



heat he shows, and quotes cases in which people work exposed to the 

 hottest sun, or under artificial conditions in temperatures far higher 

 than that of any climate in the world, but nevertheless never suffer 

 from the disease. Animals have been subjected to heat so intense 

 as to cause their death, but they have not shown the symptoms of 

 siriasis. The geographical distribution of the disease gives very 

 strong support to Dr Sambon's theory. For true sunstroke is quite 

 absent from many areas where the sun's heat is exceptionally power- 

 ful, as on the dry plains of Colorado, while it is prevalent in low, 

 damp regions, such as the Mississippi valley, where the actual 

 temperature is lower. In India again, it is common on the low- 

 lying plains of the Ganges, but is unknown on the higher central 

 plateau where the sun's power is much greater. Another argument 

 in favour of the organic origin of the malady is the fact that it comes 

 in epidemics, which often decimate hospital wards, where the patients 

 are protected from the sun, and are less fatal among men working 

 exposed to the full fury of the sun. Dr Sambon compares the 

 bacterium to that of tetanus, for he considers that it lives in the 

 soil, and is carried with dust either into the lungs or alimentary 

 canal, where it forms a toxic poison which is the actual instrument 

 of death. Dr Sambon's suggestive paper shows how little is yet 

 known regarding some of the most fatal of tropical diseases, the 

 further study of which is a duty on the part of the nation, which is 

 responsible for the administration of so large a proportion of the 

 tropical regions. 



The Effect of Aquatic Plants on Water Supplies 



Now that the legislature throws upon our urban and district 

 councils the onus of providing ' pure ' water, the study of every- 

 thing affecting either the purity or palatability of water has assumed 

 great practical importance. As a broad fact it is doubtless true 

 that the growth of green plants in water causes the water to be 

 oxygenated and makes for purity. It has been known for some 

 time that the growth of certain low forms of vegetable life in 

 water is capable of imparting to it a disagreeable odour owing 

 to the impregnation of the water by bodies resembling essential 

 oils. Thus it is recorded by Dr Thresh, that in 1891 the water 

 of Bolton in Lancashire acquired a ' fishy ' odour and taste owing to 

 the growth of a certain fresh-water alga, and a similar accident 

 happened at Cheltenham in the same year. 



The latest addition to our knowledge on this subject comes from 

 Massachusetts in a paper by Messrs Jackson and EUms, who are 

 respectively assistant biologist and assistant chemist to the State 

 Board of Health. 



In 1895 an abundant growth of Anabaena, one of the Cyano- 



