ULTRA-VIOLET LIGHT 547 



(3) Where does the yeast protoplasm get material for growth ? 



(4) Wliero (loos veast ])r(it()plasm get the energy for growth ? 



55. Mimicry of Cell Structure (Herrera after Harthig). 



A crystallising dish 18 cm. in diameter is filled with colloidal silica. This 

 may readily be prepared by dissolving freshly precipitated gelatinous silica in a 

 solution of ammonia (density 26°). Silica is added till all the ammonia has 

 been driven off and the colloid has a density of over 1-032 [i.e. 3-5 per cent, 

 solid silica). (A solution of sodium silicate of a density of l-02() may be 

 used instead of colloidal silica.) At one edge of the crystallising dish place 

 10-20 mgrm. of recrystallised potassium bifluoride. At the diametrically 

 opposite side of the dish place 5 gm. pure powdered anhydrous calcium 

 chloride. Cover and keep at 20° C. for 24 hours. Various structures which 

 nuiy be stained by any of the dyes used by histologists may be seen, '.g. 

 nucleated amoebae, cells undergoing division, nuclear spiremes, granular 

 and honeycomb structures, etc. 



The figures are due to the strains produced in the silicate by the simul- 

 taneous JFormation of a colloid, calcium silicate and a crystalloid, calcium 

 fluoride. Silica, coagidated by a crystalloid, gives rise to a semipermeable 

 membrane, which, if it forms a sac round a crystalloid, may set up endos- 

 mosis. Slow amoeboid movements may be shown by some of the complexes 

 lying near the point of insertion of the CaCU. Add a trace of alcohol over 

 the CaCU. and more ra]5id diffusion ensues. 



56. Action of Ultra-violet Light. 



The light used is passed through a Wood's filter which cuts ofT all the 

 visible rays. Caution must, therefore, he exercised to prevent any of the direct 

 rays from enter inq the eye. If an adequately screened lanij:) like the K.B.B. 

 microscope lamp is used, goggles need not be worn. With unscreened lamps 

 thev are essential. 



(a) To render the rays visible. Thin glass test tubes may be used, but 

 better results are obtained with flat-sided quartz vessels. Place vessels 

 containing solutions of fluorescent substances in the rays and about a foot 

 away from the Wood's filter. Try quinine, eosiu, fluorescein, and dilute 

 hsematoporphyrin. 



It is interesting to note the beautiful fluorescence obtained with " natural " 

 pearls and the absolute lack of it with imitations. " Cultured " pearls vary. 

 They all fluoresce, and some of them are almost as fluorescent as the " natural" 

 pearl. 



{h) Bleachina effect. Expose the following solutions for one minute at 1 ft. 

 from the lamp. Acetone-methylene blue, 20 per cent, potassium ferro- 

 cyanide, carbon-tetrachloride -f potassiimi iodide. Rays below 2,650 A° 

 cause the liberation of nascent chlorine from the tetrachloride. The chlorine 

 replaces the iodine in the KI. The iodine thus set free gives the tetrachloride 

 a reddish violet tinge. 



Filter paper if soaked in potassium ferrocyanide is bleached, and if soaked 

 in paraphenylenediamene nitrate turns violet on exposure to the short rays. 



(c) Schanz' experiment. A dilute solution of egg albumin exposed for an 

 hour in a quartz vessel close to the lamp (within 5 cm.) is so changed in 

 colloidal state that it acts to half-saturation with ammonium sul])hate like a 

 globulin, 'i.e. it tends to lose its emulsoid character and become more like 

 a suspensoid. It ceases to protect gold (Experiment 37). 



{d) Effect on enzymes. Expose an active solution of any of the digestive 

 enzymes for an hour near the lamp and comy)are their activity with that of 

 some of the unexposed solution. Maltase reacts very rapidly. 



35—3 



