428 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The amount of each metal which will kill fish is always much less 

 than that required to prevent the development of bacteria. The 

 marked poisonous action of ammonium, lithium, and potassium on fish 

 and all animals is in striking contrast to the slight effect which these 

 metals exert on plants and bacteria. Poisons may be divided into two 

 classes, viz. general poisons, of which mercury is the most potent, 

 which even in small quantities have a deleterious action on both plants 

 and animals ; and special poisons, such as potassium and ammonium 

 salts, and the alkaloids, which are injurious only to animals, and exert 

 little or no poisonous action on plants. The difference is probably 

 due to the fact that poisons of the second class act only on nerve-cells, 

 whereas those of the first class act on all cells. Possibly the action 

 of ammonium and potassium salts may serve to distinguish between 

 plants and animals in the lower forms of life. 



Micro-organisms in Soils.* — Prom examinations of a large number 

 of samples, K. Koch found that the superficial layers of soil were very 

 rich in germs of bacteria, particularly in bacilli. Micrococci were 

 only found in places which had not been cleansed from decaying 

 matter ; the latter perished on heating the samples, but the bacilli did 

 not, being mostly in the condition of spores, and it appears probable 

 that they are introduced by means of manures and household offal. 



The quantity of micro-organisms diminishes very rapidly with 

 increase of depth, so that at the distance of one metre from the surface 

 the earth is very free from them. P. Miquel attempts to estimate the 

 number present in one gr. of soil, taken from a depth of • 20 metre 

 from the surface, and found in three samples : from Montsouris, 

 700,000 organisms ; Gennevilliers, manured with liquid sewage, 

 870,000 ; Gennevilliers not so treated, 900,000. 



The office of these minute organisms appears to be of great 

 importance in the transformation of substances to forms suitable for 

 plant-food. 



Bacteria and Microscopical Algse on the Surface of Coins in 

 Currency. — Prof. P. P. Keinsch writes us as follows : — " Accidentally 

 induced to examine microscopically the surface of a small silver coin, 

 I made the observation of the presence of numerous Bacteria and 

 microscopic unicellular algae living in the incrustations and sediments 

 which have been produced through constant use. I examined coins 

 of various nations and of various value, and found my first observa- 

 tion perfectly confirmed. All silver and copper coins, several years 

 in currency, show this curious vegetation of organisms of the lowest 

 rank. It is observed best on coins twenty to thirty years old. 



To observe this life, a small quantity of the sediment adhering to 

 the prominences and in the cavities of the surface of the coin is 

 scratched off with the top of a knife and put in a drop of distilled 

 water on a slide, spread out in the water and immediately covered 

 with a cover-glass. 



Between the agglomerations of larger and smaller granules, scarcely 

 dispersed fragments of fibres, and especially numerous granules of starch 



* Bied. Centr., 1883, pp. 581-2. Cf. Journ. Chem. Soc— Abstr., xlvi. (1884) 

 p. 486. 



