The Permeability of Cells for Acids. 149 
0.5, 0.6, 0.7, 0.8, 1.0, and 1.2 ¢.c. n/10 acid, and the concentration noted 
in which movement of the cilia ceased in 20 hours. To make sure that 
the cilia had been really killed and not simply stopped by the acid, as 
observed by Barratt’ on Paramecium, it was found necessary to stim- 
ulate them mechanically. 
In table 2 the acids with nearly the same effect or property are 
arranged in groups and in an order to correspond as nearly as possible 
with the penetration series. An asterisk marks the acids which are 
markedly out of place in the series. The following acids were studied: 
Benzoic, CsH; COOH = Benz. 
o-Salicylic, CsHsOH COOH = Salic. 
(o-Amino benzoic, CsH4NH2 COOH). 
Formic, HCOOH = For. 
Acetic, CH; COOH = Acet. 
Propionic, CH; CH2 COOH = Prop. 
n-Butyric, CH; CH2 Ch, COOH = Buty. 
iso-valeric, (CH3)2 CH CHz COOH = Val. 
(Caproic, CH; CH2 CHz CHz CHz COOH). 
Monochloracetic, CH2Cl COOH = Monoc. 
Dichloracetic, CHCl COOH = Dic. 
Trichloracetic, CCl; COOH = Tric. 
Hydrochloric, HCl = Hydroce. or Cl. 
Nitric, HNO; = Nitr. or NOs. 
Sulphuric, H2SO, = Sulph. or SO,. 
Phosphoric, HsPO4 = Phos. or PO. 
Oxalic, (COOH): = Oxal. 
Malonic, CH2(COOH): = Malon. 
(Succinic, C2Hy (COOH):). 
Glycolic, CH,0H COOH = Glycol. 
d-and I-Lactic, CH3;CH OH COOH = Lac. 
Il-Malic, CH:CHOH (COOH): = Mal. 
d-Tartaric, CHOH CHOH (COOH): = Tart. 
Citric, CH, CHOH CH: (COOH); = Cit. 
Maleic, CoH. (COOH)2 = Maleic. 
Fumaric, C.H2 (COOH), = Fum. 
The toxicity and effect of acids on many biological processes has been 
worked out, and for the sake of brevity the results have been condensed 
and recorded in table 3 for ready comparison with the results in table 2. 
It will be noted, from table 3, that there is no agreement between the 
series of acids arranged in order of efficiency in affecting various tissues. 
Take, for example, toxicity. We might expect different organisms to 
vary in resistance to the same acid but the series of acids should be the 
same. That is, however, not the case, as a comparison of the toxicity 
for Paramecium, for Lupinus seedlings, and for the cilia of the giant 
clam (table 2) will show. We can, therefore, state relations in only a 
very general way. There is a general relation between the toxicity 
for Lupinus and the giant clam, but it is not exact. 
Similarly, exceptions are noted when we compare the physiological 
effect of the acids with their physical properties. One of the closest 
parallels is between the efficiency of an acid in causing membrane 
formation in the egg of the sea-urchin and its effect in lowering the 
1Zeit. f. Alleg. Physiol., 4, p. 441, 1904. 
