246 SUSCEPTIBILITY AND IMMUNITY. 



result from the introduction into the bodies of susceptible animals of 

 the toxic substances produced by certain pathogenic bacteria. The 

 first satisfactory experimental evidence of this important fact was 

 obtained by Salmon and Smith in 1886, who succeeded in making 

 pigeons immune from the pathogenic effects of cultures of the bacil- 

 lus of hog cholera by inoculating them with sterilized cultures of 

 this bacillus. In 1888 Roux reported similar results obtained by in- 

 jecting into susceptible animals sterilized cultures of the anthrax 

 bacillus. Behring and Kitasato, in 1890, reported their success in 

 establishing immunity against virulent cultures of the bacillus of 

 tetanus and the diphtheria bacillus by inoculating susceptible ani- 

 mals with filtered, germ-free cultures of these pathogenic bacteria. 



In 1892 Behring, Kitasato, and Wassermann published the re- 

 sults of interesting experiments with a bouillon made from the 

 thymus gland of the calf. They found that the tetanus bacillus cul- 

 tivated in this bouillon did not form spores and had comparatively 

 little virulence. Mice or rabbits inoculated with it in small doses 

 0.001 to 0.2 cubic centimetre for a mouse proved to be subsequently 

 immune. And the blood serum of an immune rabbit injected into 

 the peritoneal cavity of a mouse 0.1 to 0.5 cubic centimetre was 

 found to give it immunity from the pathogenic action of a virulent 

 culture of the tetanus bacillus. Similar results were obtained with 

 several other pathogenic bacteria cultivated in the thymus bouillon- 

 spirillum of cholera, bacillus of diphtheria, typhoid bacillus. We 

 give here the directions for preparing the thymus bouillon as used by 

 the authors named : 



Two or three thymus glands are chopped into small pieces immediately 

 after they are taken from the animal. An equal part of distilled water is 

 added to the mass and stirred for some time ; it is then placed in an ice chest 

 for twelve hours. The juices are now expressed through gauze by means of 

 a flesh press. A clouded, slimy fluid is obtained, which constitutes a stock 

 solution. This is diluted with water, and a certain quantity of carbonate of 

 soda is added to the solution before sterilization. By this means coagulation 

 and precipitation of the active substance from the thymus gland are avoided. 

 The exact amount of water and of sodium carbonate required to prevent pre- 

 cipitation must be determined by experiment, as it differs for different glands. 

 Usuall v an eoual portion of water and sufficient soda solution to turn litmus 

 paper feeblv blue will give the desired result. The liquid is now heated in 

 a large flask, which is left for fifteen minutes in the steam sterilizer. The 

 liquid is allowed to cool and then filtered through fine linen to remove any 

 suspended coagula ; the filtrate has a milky opalescence. It is now placed 

 in test tubes and again sterilized. The active principle is precipitated by the 

 addition of a few drops of acetic acid. 



In Pasteur's inoculations against hydrophobia, made subsequently 

 to infection by the bite of a rabid animal, an attenuated virus is in- 



