1gr4] HOYT—COLLOIDAL METALS 201 
two minutes (figs. 2, 3). Under the latter conditions the modified 
outer layer frequently became ruptured, breaking away from 
the wall in purple, gelatinous masses and leaving the remainder 
of the wall and the other portions of the cell uncolored and 
apparently unaffected. Filaments of S. decimina formed swollen 
sheaths in the gold solution itself similar to those formed by 
S. longata when transferred from this solution to water. After a 
top “age 
Fic. 2 Fic. 3 
Fics. 2 and 3-—Spirogyra longata from same material as that shown in fig. 1, 48 
hours after transfer to colloidal gold solution; examined and drawn in distilled water. 
sheath had broken from a portion of the wall, no new sheath was 
formed, the rest of the wall remaining unswollen and uncolored 
during the period of the experiments (2-6 days). The results of 
further studies upon the formation of these gelatinous sheaths are 
Presented in table V. Where difficulty was experienced in deter- 
mining by simple microscopic observation whether or not swelling 
of the outer wall had occurred, such difficulty was removed by 
treatment of the material with 
Bismarck brown, which so stains TIAA A AT 
o render ture (72 days old) in o.1 per cent Crone’s 
€ven very thin sheath layers solution, 48 hours after transfer to col- 
Clearly discernible. loidal gold solution; examined and drawn 
Sheaths were formed in the apogee dees 
gold solution by Spirogyra longata from the stock culture (V, 14), 
and by S. decimina (V, 1c), and they were produced to a very 
slight degree by a species of Oscillatoria (V, 1d). No sheaths 
were thus formed upon filaments of S. longata (fig. 4) which 
had been for 72 days in o.1 per cent Crone’s solution (V, 10), 
nor by a species of Hormidium (V, re). Sheaths failed to appear 
upon S. longata in colloidal gold solution diluted with an equal 
Volume of non-toxic water (V, 2), nor were they evident upon 
