3IO W. C. ALLEE AND J. F. SCHUETT. 



that after having been twice used, the suspension required as 

 much colloidal silver as was used in a fresh suspension to bring 

 it to the same color. Similar results were obtained from other 

 experiments, and additional evidence on this point will be pre- 

 sented shortly in connection with another aspect of the subject. 



The work of Bresslau is of interest here. He finds that proto- 

 zoa give off a substance which he calls " tektin," a mucin-like body. 

 This is given off in greater abundance when the animals are 

 stimulated by heat, pressure, methylene blue or iodin, etc. The 

 " tektin," when given off, takes up water rapidly and exhibits 

 strong surface activity, adsorbing foreign particles readily. Bres- 

 slau tells of putting 2 cc. of liquid from a culture of infusoria 

 (either Colpidium or Pa/rameciuwi) containing many individuals 

 in one dish and a similar amount from the same culture, but with 

 few individuals, into another. Into each he introduced one cc. 

 of one per cent, solution of methylene blue. Both produced the 

 " tektin " and adsorbed this poisonous material, that with the many 

 animals so much more completely that the possibility of surviving 

 the toxic action of the poisonous material was greatly increased. 



CONCERNING THE SPECIFICITY OF MASS PROTECTION AGAINST 



COLLOIDAL SILVER. 



Drzewina and Bohn (19210.) in discussing the protection fur- 

 nished by masses of tadpoles of Rana fusca exposed to the action 

 of colloidal silver, as compared with isolated individuals similarly 

 treated, say : " Nous cherchons a preciser la nature des substances 

 protectrices, at a voir en particulier si elles sont specifiques," but 

 they do not present data on this point. 



There are two types of specificity possible. The protective 

 secretion may have no other function and so be specific in that 

 sense or it may be limited in protection to the species producing it. 

 The first type of specificity will be discussed later. The latter 

 aspect was investigated by placing one animal in a restricted 

 volume of water containing a number of animals of a different 

 species. All our observations show that the protective action of 

 the mass is not limited to a given species. This is what would be 

 expected if the fixing of the colloidal silver in some manner is the 



