56o FILTERABILITY OF MICRO-ORGANISMS 



filtered out. Evidently the calcium carbonate and silica neutralized each other. If, 

 however, the filter was made so that the core was a Berkefeld filter with a cortex of 

 plaster of Paris poured over this, so that the contact of materials was only at the joint 

 surface, it was found that dyes and colloids of both positive and negative charge could 

 be removed by filtration through this apparatus. The outer layer of plaster of Paris 

 removed the acidic or negative particles, the Berkefeld siliceous core removed the 

 basic or positive ones. It was also found that one could increase the efficiency of the 

 basic or gypsum filter by incorporating in the plaster of Paris up to 25 per cent of 

 magnesium oxide, calcined at i30o°C. 



Experiments have been made with so-called "filterable" micro-organisms and 

 viruses that were available, and a concise report of these experiments is appended. 

 The bacteriophage of Staphylococcus aureus which passes through the Berkefeld filter 

 does not pass the filter of plaster of Paris. The Vibrio percolans of Mudd which 

 passes through the Berkefeld filter does not pass the gypsum filter. Vaccine virus and 

 the virus of rabies do not pass through this filter. 



The following tests were made by Mr. H. H. Allard, of the United States Depart- 

 ment of Agriculture, with the sap of mosaic-diseased tobacco filtered through several 

 types of gypsum filters : 



Test I. — Ten plants inoculated with the unfiltered mosaic sap; 9 plants became diseased. 



Test 2. — Ten plants inoculated with material passed through a Berkefeld plus plaster of 

 Paris filter; none became mosaic diseased. 



Test 3. — Ten plants inoculated with virus passed through plaster of Paris filter alone; 

 none became diseased. 



Test 4. — Ten plants inoculated with mosaic sap filtered through a filter made of plaster 

 of Paris plus 2 per cent calcium carbonate (CaCOj) ; none became diseased. 



On May 29 these same filtrates were again used with the following results: 



Ten plants inoculated with the unfiltered mosaic sap gave 7 plants with mosaic disease. 



Ten plants inoculated with the sap filtered through a Berkefeld plus plaster of Paris 

 filter; none became diseased. 



Ten plants inoculated with plaster of Paris filtrate; none became diseased. 



Ten plants inoculated with sap filtered through a filter made of plaster of Paris plus 2 

 per cent calcium carbonate (CaCOj) ; none became diseased. 



It was also found that we could remove various bacterial toxins by filtration. 

 Diphtheria toxin — and by this I mean standard toxin of the United States Hygienic 

 Laboratory — when filtered through a filter made of a mixture of plaster of Paris with 

 25 per cent magnesium oxide calcined at 1300° C. had its toxic principle removed. 

 The following series of experiments illustrates this: 



390-A (Control). — November 30, 1926, 2:00 p.m., Guinea pig, weight 400 gm., received 

 diphtheria toxin 10 M.L.D. subcutaneously. Dead, December i, 1926, 6:00 p.m. Autopsy 

 showed diphtheria. 



390-B. — November 30, 1926, 2 :oo p.m., Guinea pig, weight 460 gm., received subcutane- 

 ously i-cc. diphtheria toxin containing two L-l- doses or ioo-|- M.L.D. which had been 

 filtered through a filter made of plaster of Paris +25 per cent MgO. 



391. — Guinea pig, weight 420 gm., received 2 cc. = 2oo+ M.L.D. or four L4- doses of 

 diphtheria toxin which had been filtered through a filter made of plaster of Paris -|- 25 per 

 cent MgO. 



