FILTERS. 45 



temperature of an oven in which bread is baked). The reason for this lies in the fact 

 that in three or four days time certain small organisms are able to grow through the 



walls of the filter and make their appear- 

 ance in the filtered fluids on the other 

 side. Persons who never bake their 

 water-filters rest in unwarranted secu- 

 rity. The bougies must also be handled 

 with great care and inspected carefully 

 after each baking for the appearance of 

 minute cracks. To detect cracks, im- 

 merse the tube in water and blow into 

 it. Clogged filters should be sent to 

 the firers of china, where they may be 

 purified by heating to dull redness. 



ANIMAL FLUIDS. 

 BEEF-BROTH. 



(a) Acid, neutral, and alkaline. 



(b) The same, with addition of 0.5 

 per cent c. p. sodium chloride and i per 

 cent peptone (Witte's peptonum siccum, 

 Merck's brown peptone, Savory & 

 Moore's brown peptone, etc.). This is 

 ordinary peptonized beef-broth. 



Examine as in case of plant juices. 

 The term peptone, as it occurs in bac- 

 teriological literature, usually means 

 commercial peptone, which is a mix- 

 ture of true peptone and various pro- 

 teoses or albumoses. It is therefore 

 generally best to specify just what pep- 

 tone is used. The writer now gen- 

 erally uses Witte's dry white peptone. 

 Savory & Moore's brown peptone from 

 p- 4 1 * flesh is very good for some purposes. 



*Fic. 41. Dr. Roux's pressure-filter, made by Maison Wiesnegg (P. Lequeux), Paris. The 

 working capacity of this filter is about 1.3 liters. The principal parts are : A, tube for connection 

 with compressed-air system; B, cut-off; C, cover held in place iby strong bolts ; D, central reser- 

 voir; E, cut-off; F, screw collar which holds the 'bougie in place; G, heavy 'inetaJ cylinder surround- 

 ing the bougie ; H, cut-off, which is closed of course when the apparatus is in use ; I, funnel 

 through which G and D are filled ; K, device for sterilizing the interior of the apparatus by steam 

 under light pressure (it consists of a copper chamber partly full of distilled water, to the bottom 

 of which the Bunsen flame is applied; the chamber may be unscrewed and removed) ; L, button 

 which is unscrewed to fill the chamber with water (in its center is a steam safety valve acting 

 under feeble pressure) ; M, valve which cuts the steam-generator out of the general circulation 

 when fluids are being filtered; N, tripod-top on which the apparatus turns freely. Height, 33 inches. 



