374 E,. Newton Harvey 



of COo. The increase of permeability on stimulation removes the 

 condition which is preventing the contraction. The movements 

 of sensitive plants can best be explained as due to an increase in 

 permeability of the cell membranes relative to the turgor main- 

 taining substances. The important point is that processes in 

 general brought about by stimulation are connected w^ith changes 

 in permeability." Morgan expressed the situation clearly when 

 he compared the means of causing development to a stimulus. 



The best method of determining permeability changes is by 

 the use of pigment containing cells, such as red blood corpuscles. 

 The escape of haemoglobin serves as an indicator of increased 

 permeability. This process of haemolysis occurs frequently 

 in cases of organic poisoning and is manifested in living animals 

 by haemoglobinuria. In the laboratory loss of haemoglobin 

 (from erythrocytes) can be brought about in various ways, by 

 strongly hypertonic as well as by hypotonic solutions. Brah- 

 machari^** regards the laking in hypotonic media to be due to 

 some other cause than the actual rupture of the corpuscle by 

 absorption of water. High (heat laking at 60° C.) temperatures, 

 condenser discharges, and a great variety of chemical substances 

 also allow the haemoglobin to escape. Of the latter may be men- 

 tioned acids (especially fatty acids) and alkalies, glucosides and 

 alkaloids (saponin, solanin, pilocarpin), tannin and related sub- 

 stances, fat solvents (chloroform, ether, alcohol, benzol), the bile 

 salts (Na glycocholate and taurocholate), soaps, haemolysins of 

 foreign blood sera and of animal (cobra, spider, crotalus venom), 

 plant (Amanita and Helvella) and bacterial poisons. '° 



Th|; list given above coincides almost exactly with the list of 

 chemical substances starting development. As yet there have 

 been no experiments on the poisons mentioned but it is highly 

 probable that reptile, fungus, and bacterial poisons will be found 

 as efficient in causing development as Loeb has shown the bile 



2' Brahmachari, U. N.: Biochem. Journ. iv, p. 280, 1909. 



2° For a discussion of means and substances causing haemolysis, see Stewart, G. N. Journ. of Phar- 

 macology and Exp. Therapeutics, i, 1909, p. 49. Heinz, R..: Handbuch der experimentellen Pa- 

 thologie u. Pharmakologie, Bd. i, p. 392, Jena, 19C4. 



