236 TUBERCULOSIS. 



of cases of human tuberculosis. Improvement is said to 

 have taken place in a certain proportion, especially of mild 

 cases. Experiments in vitro indicate that the serum has a 

 certain effect on the vital activity of the tubercle bacilli in- 

 asmuch as they will not grow in it. Whether this amounts 

 to a bactericidal action or not, requires further investigation. 

 Proof is still wanting that Maragliano's serum can protect 

 susceptible animals against the tubercle bacillus or heal tuber- 

 culosis in animals. 



Active Immunisation by Intracellular Toxines. Koch 

 has recently (April 1897) published the results of his latest 

 researches on tuberculosis. These start from the familiar 

 fact that in a guinea-pig inoculated with tubercle, and 

 allowed to die naturally, though tubercle bacilli are found 

 in the lesions on microscopic examination, it is often im-j 

 possible to obtain cultures from these lesions. The last 

 stages in the animal's illness are thus apparently due to the] 

 absorption of the intracellular poisons, evidence for the] 

 existence of which in the bodies of dead tubercle bacilli we \ 

 have already seen. Immunisation against such poisons 

 would thus apparently be beneficial in cases of tuberculosis. 

 To isolate them is, however, a difficult matter. Tubercle j 

 bacilli, according to Koch, are protected against rapid ] 

 absorption within the body and against the action of 

 chemical solvents outside the body by the presence, in their i 

 protoplasm, of two unsaturated fatty acids, one of which is| 

 especially insoluble. To these latter the characteristic 

 staining reactions are also probably due. Koch's isolation] 

 method was as follows. Bacilli from young virulent cultures 

 were dried in vacuo. They were then well rubbed up with 

 an agate pestle and mortar, treated with distilled water and 

 centrifugalised. The clear fluid was decanted, and is called 

 by Koch "tuberculin O." The remaining deposit was 

 again dried, bruised, treated with water, and centrifugalised, 

 the clear fluid being again decanted. This process was 

 repeated with successive residues till, on centrifugalisation, at 

 last no residue remained. All the fluids were then put 

 together, and these form what Koch calls " tuberculin R."1 



