A THEORY OF INJURY AND RECOVERY. 

 III. Repeated Exposures to Toxic Solutions. . 



By W. J. v. OSTERHOUT. 

 (From the Laboratory of Plant Physiology, Harvard University, Cambridge.) 



(Received for publication, March 21, 1921.) 



In previous papers a theory is developed which enables us to predict 

 the behavior of Laminaria when transferred from sea water to toxic 

 solutions and then replaced in sea water. If the theory is sound it 

 should also enable us to predict the behavior of tissue transferred 

 from one toxic solution to another. In order to put this to a test a 

 variety of experiments was made in which the tissue was exposed 

 to several solutions in succession. 



The experiments and calculations were carried out as previously 

 described. 



/. Alternate Exposure to NaCl and Sea Water. 



The procedure may be illustrated by a typical experiment, the 

 results of which are shown in Fig. 1. 



The tissue was exposed for 20.8 minutes^ to 0.278 m NaCl, during 

 which time the resistance fell from 100 to 74.03 per cent. The tissue 

 was then replaced in sea water. The resistance at any time, Tg^, 

 after this replacement may be calculated by means of a formula which 

 has been explained in a previous paper.^ The formula may be 

 expressed as follows : 



Resistance = (4 +5)^^^j^-^j(^. -e j+Me +^[g^)+^^- 



(1) 



^ This is corrected from 20 minutes (as explained in a previous paper^) in order 

 to make it conform to the standard curve. An example of this is given in the 

 present paper in discussing the change of resistance which occurs during the 

 second exposure to NaCl. 



2 Osterhout, W. J. V., /. Gen. Physiol., 1920-21, iii, 145. 



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