§ 1] MODIFICATION OF VITAL ACTIONS 13 



Gastropoda (Dolium, Cassis, Tritonium, Natica heros) secrete 

 2% to 3% HgSO^. (LoEW.) 



To organic acids many algae are little resistant. Thus Spiro- 

 gyra and Spliseroplea die in 0.1% malic or tartaric acid after 

 30 minutes ; in 0.05% malic or tartaric acid after 24 hours ; in 

 0.01% of these same acids in a few days. Formic acid pre- 

 vents development of bacteria even in small percents — 0.05% 

 to 0.006%. On the other hand, some protoplasm has acquired 

 a resistance to organic acids. The vinegar eel — Rhabditis 

 aceti — lives in 4% acetic acid. The protoplasm of the Dro- 

 sera tentacle resists 0.23% tartaric, citric, and other organic 

 acids. 



h. Soluble mineral bases, including those of corrosive alkalies 

 and the alkaline earths : Ca, Ba, and Sr. The corrosive alka- 

 lies cause a swelling of the protoplasm, but the primary effect 

 is rather a chemical one. (Cf. Feomank, '84, p. 90.) 



The lower water animals and plants are quickly killed by 

 0.1% potassic or sodic hydrate. Thus, the movements of 

 Chara cease in 0.05% KOH in 35 minutes. Bacteria are more 

 resistant ; the limit for the typhus bacilli being between 0.10% 

 and 0.14%, and for the cholera bacillus, between 0.14% and 

 0.18%. Ascaris is still more resistant, living for 20 minutes 

 in a 2% solution of NaOH. 



CaO is still more powerful. A 0.007% to 0.025% solution 

 in bouillon kills bacilli. A 0.013% solution is fatal to algae 

 like Spirogyra. 



K2C0g kills bacteria in 0.8% to 1.0% solutions. 



NagCOg kills Ascaris in a 5.8% solution after 5 to 6 hoars. 

 (LoEW, '93, pp. 33, 34.) Fromann has discussed the histo- 

 logical changes in protoplasm after treatment in NajCOg. 



It is difficult to say whether the action of some of these re- 

 agents may not be an osmotic, rather than a chemical one. 

 The action of Na^COg, for example, as described by Fkojiann, 

 is very similar to that of NaCl, whose action is probably solely 

 osmotic. 



c. Salts of Heavy Metals. — The method of action of these 

 poisons has been accounted for upon the following grounds : 

 When amido-acids (which are found as disintegration products 

 of all animal tissues) are treated with salts of the heavy metals. 



