224 



Scientific Proceedings (128) 



all the organisms come into contact with and are phagocyted by 

 actively functioning leucocytes. 



A method has been devised for carrying out growth inhibition 

 tests with the pneumococcus by which a constant and thorough 

 mixing of leucocytes and micro-organisms is obtained during in- 

 cubation. For this purpose mixtures of serum and washed 

 leucocytes placed in small glass tubes are seeded with varying 

 numbers of pneum|ococci. All the constituents are added in 

 known quantities. The tubes are then sealed with paraffined corks 

 and attached to an agitating apparatus placed in the incubator. 



The apparatus consists of two solid wheels made of wood and 

 mounted on an axle which rests on a central pivot-bearing placed 

 midway between the two wheels. The axle is made to oscillate in 

 a vertical plane by means of an eccentric. A small motor sup- 

 plies the power, the speed being reduced to any desired rate by 

 means of a series of pulleys. A leather belt with a piece of tape 

 run through a series of slits cut in the leather serves as a holder 

 for the tubes. This is attached to the wheel. When the ap- 

 paratus is in operation, the motion given to the tubes, rotation 

 plus oscillation, serves to mix their contents thoroughly and at 

 the same time keeps all parts of the inside surface of the tubes 

 moistened. The importance of a continuous washing of the 

 tubes' contents over all parts of the inside surface is readily seen 

 since the occurrence of any drying would probably mean the 

 escape of some of the organisms from phagocytosis. Rotation 

 and oscillation are maintained at a slow rate so as to reduce to 

 a minimum mechanical injury to the leucocytes. 



The pneumococci used for the test were suspended in Locke's 

 solution P H 7.8-8.0, to which 0.125 per cent, of gelatin had been 

 added for the purpose of better preserving the organisms. The 

 suspension was standardized by means of Gates' turbidimeter 

 method with preliminary bacterial counts. A standard suspension 

 of approximately 1,000 million pneumococci was used. Dilutions 

 were made from the suspension in gelatin Locke's solution. Only 

 organisms in the active growth phase were employed in the tests. 

 The strain used was of low virulence for the cat, but highly 

 virulent for rabbits, guinea pigs and mice. The leucocytes were 

 obtained from pleural exudate produced by the injection of 

 aleuronat. The exudate was mixed in the pleural cavity with equal 

 parts of 1 per cent, sodium citrate in normal salt solution. After 



