62 Effect of Arsenic Compounds 



III. EFFECT OF ARSENIC COMPOUNDS ON CERTAIN OF THE 

 LOWER PLANTS. 



1. Algae. 



Loew (1883) was sceptical concerning the specific toxicity of arsenic 

 for plant protoplasm. He was convinced that arsenic and arsenious 

 acid were poisonous to algae, not because of their specific character as 

 arsenical compounds, but because of their acid nature, algae being 

 peculiarly sensitive to any acid, and he maintained that these substances 

 were not more poisonous than vinegar or citric acid. He placed various 

 species of Spirogyra in solutions of *2 gm. potassium arsenate per litre 

 water (1/5000), and found that the algae grew well without making any 

 abnormal growth in a fortnight, showing hardly one dead thread. Some of 

 this alga was then transferred to a 1/1000 solution of potassium arsenate. 

 This suited it excellently and it increased and the appearance under the 

 microscope was very fresh and strong, which was attributed more to the 

 potash than to the arsenic acid. Loew maintained that for the lower 

 animals and for many of the lower plants arsenic in the form of neutral 

 salts is not a poison. When the differentiation of the protoplasm into 

 certain organs reaches a specific degree in the higher plants, then the 

 poisonous action of the arsenic compounds comes into play. 



Knop (1884) found that certain unicellular green algae grew 

 luxuriantly in a neutral solution supplied with potassium arsenate. 

 Bouilhac (1894) concerned himself chiefly with the possibility of the 

 replacement of phosphates by arsenates. He recognised that the in- 

 fluence of arsenic is not the same on all species of plants, so he confined 

 his attention to certain of the algae. Stichococcus bacillaris Naegeli 

 was found to live and reproduce itself in a mineral solution containing 

 arsenic acid. Even in the presence of phosphoric acid the arsenic acid 

 favours growth, the best dose being about 1/1000. The arsenic acid is 

 capable of partly replacing phosphoric acid. Other species of algae, 

 Protococcus infusionum, Ulothrix tenerrima, and Phormidium Valderi- 

 anum invaded the original culture of Stichococcus from the atmosphere, 

 but with no arsenic or phosphoric acid their development was poor. 

 The jars with arsenic compounds were invaded by still more species 

 which grew strongly. Under these conditions it is evident that these 

 algae are capable of assimilating arsenic, and the addition of arsenic acid 

 to a solution free from phosphoric acid is sufficient to enable these algae 

 to live satisfactorily, the arsenates in this case replacing the phosphates. 

 Ono (1900) found that algae are favourably influenced by small doses of 



