304 w - c - ALLEE AND J. F. SCHUETT. 



of opinion. Drzewina and Bohn summarize their conclusions re- 

 peatedly in some such words as the following (1921 d) : "Bref, si 

 chez di verses especes que nous avons examinees jusqu'ici (Para- 

 mecies, Colpodes, Stylonychies, Stentors, Hydres, Convoluta, Glos- 

 siphonies, tetrads de Grenouille) tout se passe comme s'il y avait 

 emission rapide d'une substance ou de substances assurant une 

 defense ; chez Poly cells, c'est le contraire (against KG) : on as- 

 siste, non pas a une auto-protection mais a une auto-destruction." 



They do not believe that the greater resistance of the group is 

 due to a more rapid using up of the toxic substance, and cite two 

 types of experiments to support their contention (1921). In the 

 first type they expose some hundred (centaine) of Convoluta in 

 one suspension and two each in the accompanying dishes. Even 

 if the former receive 10 drops of colloidal silver to 25 cc. of water 

 and the isolated animals have only two drops for the same volume, 

 they find that the large group survives after the others are dis- 

 integrated. This is a fairer test than if the same amount of col- 

 loidal silver were added in both cases, but still it must be remarked 

 that the ratio of colloidal silver per individual is about 10 times 

 greater in the case of the two individuals, when compared with 

 the larger group. 



We have made some exact tests to cover this point and present 

 the following summary of our results : 



Animals Used: Planaria dorotoccphala, 15-25 mm. long, ex- 

 posed to action of colloidal silver for 7 hrs., then washed and trans- 

 ferred to water to which they were accustomed and examined on 

 the day following the exposure. 



I. 40 planarians isolated into 10 cc. of water plus 2 drops colloidal silver. 



No. % 



Normal, crawling when stimulated i 2.5 



Less than half disintegrated 2 5.0 



Half and less than two thirds disintegrated 4 10.0 



Two thirds but not all disintegrated 8 20.0 



Wholly disintegrated 25 62.5 



IT. 150 planarians in 6 lots each in 250 cc. water plus 50 drops colloidal silver. 



Normal, crawling when stimulated o o 



Less than half disintegrated o o 



Half, but less than two thirds disintegrated 18 12 



Two thirds, but not all disintegrated 5 2 35 



Wholly disintegrated 80 53 



