THE GENERAL PROPERTIES OF POISONS 261 



Sulphate of zinc is almost as innocuous to Penicillium glaucum as 

 sulphate of copper, and the plant can also withstand large quantities of 

 dissolved arsenic. On the other hand, it is hardly if at all more resistant to 

 the salts of cobalt, mercury, and thallium than is Aspergillus and other 

 mould-fungi, and Clark even states (1. c., p. 399) that it is less resistant to 

 free acids than are the latter. 



In general the salts of the heavy metals are very poisonous, and 

 especially those of silver and mercury. Manganese salts appear to be 

 feebly poisonous, although all plants are not so unaffected as is Penicillium^ 

 which only ceases growing when the concentration reaches 37-7 per cent, 

 (i gramme-molecule of MnSO 4 in 0-4 litres), whereas in ferric sulphate 

 the limit of growth is reached at a concentration of 8 per cent, (i gramme- 

 molecule in 5 litres). Sulphate of zinc is a moderately strong poison for 

 most mould-fungi, and is a very strong one for Phanerogams. 



It is usually the case that animal-poisons are plant-poisons also, 

 although it is hardly surprising that ricin, abrin, and probably other tox- 

 albumins which are deadly poisons to higher animals, are only feebly 

 poisonous to certain algae 1 . Since carbon monoxide acts as a poison 

 only by forming a non-oxidizable compound with haemoglobin, it is only 

 natural that it should not be poisonous to plants and to lower animals 2 . 

 This also applies to those pigmented bacteria which are able to absorb and 

 accumulate oxygen in the same way that haemoglobin does. There may 

 possibly be exceptions, however, and it has even been stated that hydrogen 

 exerts an injurious action on Pelomyxa palustris 3 . 



In adult organs the development of the cuticle hinders the absorption 

 of poisons, to which at the same time the protoplasm may become more 

 resistant. It is probably owing to internal changes that the spores of 

 bacteria become more resistant 4 , but those of certain fungi less resistant 

 than the vegetative parts 5 . 



The external conditions also exercise some influence, and dry organisms 

 are almost unaffected by poisonous gases, alcohol, and carbon bisulphide, as 



1 Bokorny, Pfliiger's Archiv f. Physiol., 1896, Bd. LXIV, p. 305. 



3 Kunkel (Centralbl. f. Physiol., 1900, Bd. XIII, p. 565) finds that CO is not poisonous to 

 poikilothermic Vertebrata. Cf. also Mosso, Compt rend., 1900, T. CXxxr, p. 483. 



3 Celakovsky, Bull, international d. 1'Acad. d. Sci. d. Boheme, 1898, p. 23. Perfectly 

 pure hydrogen seems to exercise no poisonous action whatever apart from the effects due to its 

 displacing oxygen. Cf. Ewart, Journ. of Linn. Soc., Vol. xxxni, 1896, pp. 403-5, and Protoplasmic 

 Streaming, 1903, pp. 39-41. To obtain absolutely pure hydrogen in large quantity is by no means 

 easy. Positive results are always due to the presence of poisonous impurities such as SO 2 , AsH 3 , 

 HC1, H 2 S, &c., in the hydrogen employed. The same remarks apply to Samassa's statement 

 (Einwirkung von Gasen auf d. Protoplasmastromung, &c., 1898, p. 12) that hydrogen acts as a poison 

 on frogs' eggs. 



* Brefeld, Unters. ii. d. Spaltpilze, 1878, p. 11 (repr. from Sitzungsb. der naturf. Freunde zu 

 Berlin); Tschirch, Das Kupfer, 1893, p. 45 ; Fliigge, Mikroorganismen, 1896, 3. Aufl., p. 451 ; 

 Kronig and Paul, Zeitschr. f. Hygiene, 1897, Bd. XXV, p. i. 



5 Clark, Botanical Gazette, 1899, Vol. xxvill, p. 400. 



