30 THE ROYAL SOCIETY OF CANADA 



mucilage was shown by allowing them to mingle while under ultra- 

 microscopic observation, when an abundant coagulation could be 

 followed, as in the case of casein when acted on by HCl. 



We may, therefore, conclude that the change in viscidity caused 

 by the dye is due to the mutual precipitation. When the dye is in 

 insufficient quantity only partial coagulation (fiocculation) accom- 

 panied by slight lowering of viscidity occurs. When the dye is in 

 sufficient quantity a continuous coagulum is formed within which the 

 viscidity is raised by syneresis. The series described parallel the 

 changes in viscosity of albumin on heating. Dyes which are not 

 adsorbed do not affect the viscidity. 



A somewhat analogous .behaviour is seen in gum acacia when 

 treated with Congo red, though towards vesuvin (electro negative), 

 methylene blue and neutral red (both electro positive) there appears 

 to be no reaction. With Congo red in constant concentration, there 

 is produced with increasing concentrations of the gum an increasing 

 turbidity, due to the formation of a brown suspension. When rendered 

 slightly alkaline, the turbidity clears away, and the clear red colour 

 of the dye is produced. ^^ With change to slight acidity, the turbidity 

 does not at once reappear. The gum is not a pure substance, but 

 contains some resin. The dye is adsorbed by filter paper, while the 

 brown suspensoid, like Congo blue, is not adsorbed. The viscosity 

 is not so easily estimated as in the case of cactus mucilage, but a 

 lowering of viscosity on the introduction of the dye was fairly evident. ^^ 



The Effects of Salts. — Spoehr (i.e.) was unable to salt out cactus 

 mucilage for chemical study. In connection with the above observa- 

 tions, I have tried the effects of a few salts to obtain prelimitiary data. 

 Solutions of the mucilage in high concentration, forming a very ropy 

 mass, were subjected to cupric chlorid, copper sulphate, iron alum, 

 barium chlorid, potassium dichromate and mercuric chlorid, in ca. 

 6 per cent solution (HgCl2, sat.) and the viscidity gradually dis- 

 appeared, but most rapidly in the copper salts, and least in the mercury 

 salt. The change occupied 12 hours to seven days, the rate being 

 approximately in the order in which the salts are named above. There 

 was, however, no evidence of clotting or fiocculation, and chemical 

 change is not excluded. 



" Cactus mucilage does not adsorb neutral red when alkaline, though it diffuses 

 through the living protoplasm and accumulates in the sap, colouring it scarlet. 



^^ I have not yet studied the behaviour in the absence of impurities (salts). It 

 will be profitable to pursue the relation of Congo red to mucilage further in the light 

 of the interesting work of Bayliss (Proc. Roy. Soc. ser. B. 84 : p. 81). 



