206 



CARNEGIE INSTITUTION OF WASHINGTON. 



cilia of the palps of the giant clam, a common bivalve moUusk of the Murray 

 Island reefs, is also included. Acids out of place as compared with the series 

 for penetration rate are marked with an asterisk. If the tissues have pre- 

 viously been killed, every acid penetrates practically instantaneously in n/100 

 concentration. 



From the data above recorded, we are justified in drawing the following 

 conclusions: 



Living cells are resistant to the entrance of all acids, with the exception of 

 salicylic and benzoic and possibly valeric. The degree of resistance 

 varies with the acid and is not nearly so marked as in alkalies. 



Dead cells are permeable for all acids. 



There is no relation l)etween the degree of dissociation of the acid and its 

 rate of penetration or between degree of dissociation and toxicity. 



There is a general relation between penetrability and solubility in xylol 

 and surface-tension lowering, but it is not exact and not quantitative. 



The best relation is between penetrability and toxicity. The acids which 

 penetrate most readily are most toxic, irrespective of their strength. 



With acids, as with alkalies, lipoid solubility^ appears to be a determining 

 factor in penetrability. If the acid is soluble enough in fatty substances, it 

 encounters no resistance at the cell surface. If it is lipoid insoluble or only 

 slightly soluble, the normal cell surface must be destroyed before it can enter. 

 The strength of the acid and possibly also a specific action of the anion on the 

 surface proteins will then determine its rate of entrance, or, better, its rate of 

 alteration of the cell surface. 



II. Cell Permeability for Alkalies. 



The permeability of marine tissues for three additional^ alkalies was deter- 

 mined, making use of the neutral-red method. 



(a) Lithium hydroxide (LiOH) behaves as NaOH, as shown in the follow- 

 ing table, which gives the times for color changes in various concentrations in 

 Mg.-free sea-water. 



There is no return of the red color in sea-water. 



(h) Piperidin behaves as does NH4OH and the amines. The same tissues 

 were tested and found to become yellow in n/250 piperidin in 1 minute. The 

 red color returns promptly on return to sea-water. 



(c) Piperazin penetrates only in relatively strong concentration, viz : 



The red color returns very slowly in sea-water. 



'Or surface tension. It is possible, as Traube holds, that ability to lower the surface tension of 

 water is the determining factor in penetration of cells. 

 "See Harvey, E. N., Carnegie Inst, Wash. Pub. No. 183. 



