3IO L. H. HYMAN. 



should have produced the same amount of depression at the 

 same hydrogen ion concentration. Reference to Table VI. shows 

 that this is not at all the case, butyric acid furnishing a notable 

 exception. According to Loeb also, di- and tri-basic acids should 

 be less effective than monobasic. This again is not upheld by 

 my results. Sulphuric acid is even more effective than hydro- 

 chloric, although being dibasic it should be only half as effective. 

 Tartaric, another dibasic acid, has about the same efficiency as 

 the monobasic mineral acids. Of course, it is not certain that 

 Loeb intended his ideas to apply to living organisms. Further 

 the hydrogen ion concentrations with which Loeb worked are 

 mostly instantly or rapidly fatal to living organisms. It remains 

 to be proved whether the statements of Loeb will hold at physio- 

 logical concentrations of acid. I have been informed that 

 Michaelis has publicly stated that they do not hold and that the 

 Hofmeister series remains unshaken. From the fact that in my 

 experiments different acids produce different degrees of depression 

 at the same hydrogen ion concentration it appears necessary to 

 conclude that the hydrogen ion concentration is not the principal 

 factor in the result. 



(/) When a certain degree of acidification has been attained, 

 further acidification does not increase the percentage of depres- 

 sion. The percentage of depression obtained at pH 5.0 is about 

 the maximum that can be produced without actual injury to 

 the animals. It appears that a depression of 50 per cent, is the 

 most that can be obtained with any acid on the average. Of 

 course individual experiments may yield a depression slightly 

 greater than this. A depression of 58 per cent, is the greatest 

 recorded in the dozens of experiments performed with the various 

 acids and this figure was obtained on young worms. The state- 

 ments in this paragraph apply only when an ample supply of 

 oxygen is present in the water. 



(g) The decrease in the rate of oxygen consumption reaches 

 its maximum value for any particular concentration during the 

 first hour of exposure to the acidified water. Prolonged exposure 

 does not increase the depressing effect. On the contrary there 

 is generally some slight rise in the oxygen consumption during 

 several hours exposure. This is too small however to be con- 

 sidered of significance. 



