74 BACTERIOLOGY. 



taking tetanus toxin as an example, it may be said that 

 in aqueous solution it is not coagulated by heat, but is 

 in time deprived of its poisonous qualities. The addi- 

 tion of small quantities of acids or alkalies to the solu- 

 tion, and the continued passage through it of carbon 

 dioxide or sulphuretted hydrogen, distinctly reduce its 

 toxicity. When exposed to light and air, either in a 

 dry state or in solution, the toxin deteriorates rather 

 rapidly. It withstands a temperature of 70 C. for 

 some time without being wholly destroyed ; higher 

 temperatures decompose it rapidly. When protected 

 from the light and air it is slowly converted into an in- 

 active substance; it is better preserved under absolute 

 alcohol, pure ether, and the like. The toxicity of the 

 purest tetanus toxin now obtainable is almost incred- 

 ible : 0.00005 milligramme of it kills a mouse of 15 

 grammes; a man of 150 pounds weight, if he were equally 

 susceptible, would be killed with 0.23 milligrammes. 

 It requires 30 to 100 milligrammes of strychnine to 

 kill a man under ordinary circumstances. The most 

 virulent diphtheria bacilli produce a specific poison 

 which does not fall far behind that of tetanus in power. 

 Sulphuretted Hydrogen. Sulphuretted hydrogen is a 

 very common bacterial product. Its presence is deter- 

 mined by pasting a piece of paper moistened with lead 

 acetate inside the neck of the flask containing the cul- 

 ture, closing the mouth with a cotton-wool stopper, and 

 over this again an India-rubber cap (black rubber free 

 from sulphur). The paper is colored at first brownish 

 and later black; repeated observation is necessary, as 

 the color sometimes disappears toward the end of the 

 reaction. Apparently negative results should not be 

 rashly accepted as conclusive. 



