RETARDING INFLUENCE OF CROWDING 125 



Goetsch' on the effect of stimulation by contact with the walls of a 

 small container in limiting the growth of active animals, even though 

 the contained liquid be effectively connected with that of a much 

 larger vessel. 



Undoubtedly there may be a limiting toxic effect of materials 

 leached out of glass, particularly from soft glass. The dangers result- 

 ing from the use of such glassware have been known for years. In ad- 

 dition there may be a physical as well as a chemical effect from the 

 glass walls of an inclosing vessel. Such effects are shown in the recent 

 work of Drzewina and Bohn (1927). They base their experiments on 

 the report of Norrish (1924, vide Taylor), who found that bromine 

 combines with ethylene about twice as fast in contact with a surface 

 of stearic acid as with one of glass, and that, on the other hand, the 

 reaction within a paraffin-lined dish is about one-thirtieth of that 

 given when the exposed surface is one of stearic acid. Using the 

 marine flatworm Convoluta, Drzewina and Bohn found that these 

 small worms survive only about half an hour when placed in sea 

 water in a glass dish coated with stearic acid. In this instance the 

 worms are not affected by dissolved chemicals, since stearic acid is 

 insoluble in water. There is no change in the pH of the water, and 

 water which has stood in such dishes is non-toxic when removed. A 

 glass dish coated with paraffin becomes less toxic than is a plain glass 

 dish. If the Convoluta in a glass dish on a white background are ex- 

 posed to sunlight, they do not maintain their normal activity so 

 long as when they are in a paraffined dish. There is also greater pro- 

 tection in the latter against the toxic action of metallic silver. Para- 

 mecia behave similarly. They die more rapidly in a dish covered with 

 stearic acid, whether in light or in shade. Paraffin protects them 

 against the action of metallic silver and of neutral red, even though 

 they take up as much neutral red in a paraffined dish as in a plain 

 glass dish. Drzewina and Bohn conclude that stearic acid catalyzes 

 reactions of living animals but that paraffin inhibits them. They sug- 

 gest that the action is similar to the action of paraffined glass in 

 preventing the coagulation of blood, and advance the theory that 



' It is not yet definitely proven by chemical tests that the tubes with one end covered 

 by cloth do allow free diffusion of excretory products. 



