52 BIOLOGY OF PNEUMOCOCCUS 



Swift's 1370 method is a successful example. The culture is scraped 

 from the surface of the solid medium, spread in thin layers on 

 plates or in tubes, and quickly frozen. The frozen material is then 

 placed in a chilled Hempel desiccator containing phosphorus pent- 

 oxide in the bottom and sulfuric ether in the moat. The drawing 

 of a high vacuum dissipates the frozen moisture, and the resulting 

 dry powder, if kept anhydrous, is found to contain viable organ- 

 isms after many months of storage. Later, Otten, 1040 using a simi- 

 lar method for drying thick suspensions of pneumococci in salt 

 solution, reported their recovery in living condition after long pe- 

 riods of preservation. Desiccated cultures, unlike those on moist 

 media, can be shipped over distances involving many days' expo- 

 sure to wide temperature variations. 



The reader who desires further details concerning the preserva- 

 tion of bacterial cultures is referred to the communication of Flos- 

 dorf and Mudd 454 who, after reviewing the literature on the sub- 

 ject, described an apparatus for the rapid drying and preservation 

 of bacteria, serum, and other biological substances. The method 

 consists in applying a high vacuum to the material to be dried 

 rapidly and freezing it by immersion in a bath chilled to — 78° by 

 the use of Dry-Ice and Methyl Cellusolve. 



Another practical method for having virulent cultures at hand 

 is that devised by Neufeld 1000 based on the principle earlier estab- 

 lished by Heim. Pieces of spleen or heart or the whole organs of 

 mice dead of experimental pneumococcal infection are placed in 

 open Petri dishes or in small tubes loosely plugged with cotton and 

 dried in a vacuum desiccator over calcium chloride or concen- 

 trated sulfuric acid. To recover the pneumococci, generous pieces 

 of the dried organs are ground in a mortar with broth, and the sus- 

 pension injected intraperitoneally into a mouse. The heart's blood 

 of the dead or dying mouse usually yields a pure, virulent culture. 



Autolysis 

 Pneumococcus is a delicate organism and may rapidly disinte- 



