58 



PHYSIOLOGY OF NUTRITION 



Liquids may also be sterilized by filtration. The most convenient arrange- 

 ment for this purpose is the Chamberland filter, a hollow cylinder of porous 

 porcelain, closed at one end. The liquid to be sterilized is passed, under pres- 

 sure, through the porous walls of the previously sterilized filter. 



Various disinfecting materials are also used for the chemical destruction of 

 microorganisms. The most effective of these is corrosive sublimate, or mercuric 

 chloride (HgCl 2 ). A solution of i g. of mercuric chloride in a liter of distilled 

 water is thus used in bacteriological laboratories. The hands of the worker and 

 also his implements are disinfected with this solu- 

 tion, which is also employed to destroy cultures 

 that are not needed. A solution of one part of 

 the salt in 300,000 parts of water prevents the 

 development of the bacillus of splenic fever, 

 Bacillus anthracis. Sulphurous acid, chlorinated 

 lime [also known as bleaching powder; it con- 

 tains calcium hypochlorite], hydrofluoric acid 

 and its salts, boric acid, ozone, hydrogen per- 

 oxide, milk of lime, and phenol, or carbolic 

 acid, are also suitable for use as disinfectants/ 

 §6. Pure Cultures. — To study microorgan- 

 isms with respect to their developmental history 

 and their physiological process it is necessary 

 to 1 ' obtain them in a pure culture. 1 A pure 

 culture is one known to contain only a single, 

 definite species of organism. Such a culture 

 can be obtained only by fulfilling two conditions. 

 The first consists in the exercise of sufficient 

 precaution to prevent the entrance of germs 

 from the air into the sterilized culture medium; 

 the second is the derivation of the culture from 

 a single cell. A culture in which all the micro- 

 organisms are quite similar is nevertheless not 

 to be termed a pure culture unless it has been derived from a single cell, 

 since very many microorganisms with entirely different physiological properties 



1 Pure cultures may be purchased irom several establishments, among which may be mentioned the 

 following: Krals Bakteriologisches Laboratorium, Prag I, Kleiner Ring II; Institut für Gärungsgewerbe, 

 Berlin N, Seest:asse 65; Jörgensens Laboratorium, Kopenhagen, Frydendalsvej 30; Zentralstelle für Pilz- 

 kulturen, Amsterdam. [They may be obtained from the Laboratory of the American Museum of Natural 

 History, New York, and from Parke, Davis and Co., Detroit.— Ed.] 



e To the substances mentioned in the text may be added: iodine, sodium sulphite and 

 Dakin's recent discovery, paratoluene-sodium-sulphochloramide (on the American market 

 under the trade-name chlorazene, though it was called "chloramine" by Dakin [British 

 med. jour., Aug. 25, 1915, also Jan. 29, 1916]). Chlorine, bromine, and potassium per- 

 manganate are also used as disinfectants. It should be noted, however, that antiseptics 

 or disinfectants that are useful in some cases may be useless or even harmful in others. 

 Numerous references on this subject are given in the Index Medicus, Carnegie Inst., Wash. — 

 Ed. 



Fig. 35. — Autoclave. The top 

 is hinged and may be raised after 

 releasing the locking clamps. 



