In spite of a call upon him for his every waking hour, he 01 ^ 

 made a new discovery. He had already observed how the dif- 

 ferent organisms to which he had applied himself needed for 

 optimal growth an exact concentration of oxygen. Now he 

 found them equally dependent upon an exact concentration 

 of carbonic acid gas (CO2, as the boys call it). The bygone 

 year had showed "that if the respiratory CO2 evolved by a 

 freshly-planted virulent culture of the tubercle bacillus was 

 removed, growth did not take place." The bacilli, though 

 alive, remained in a non-reproductive state. His (four-page!) 

 article [61] detailed quantitative study of the question. He 

 made implantations of the tuberculosis germ from two dif- 

 ferent strains into test tubes in the regular fashion. But now 

 he hitched these tubes by means of a tightly fitting rubber 

 hose to a second, containing a fluid which would or would not 

 suck up the carbonic acid gas as produced in the growth- 

 process of the organism. When water merely was thus em- 

 ployed, the tubercle bacillus grew luxuriantly (because the 

 CO2 it produced accumulated and was not absorbed by the 

 water) ; but when an alkali of some sort was added to this 

 water (Wherry used barium hydroxide or sodium hydroxide) 

 they grew hardly at all. But neither too much nor too little 

 of the CO2 might thus be allowed to stagnate in the atmosphere 

 about the organism. Its total absence was inimical to growth; 

 but thirteen percent of it, also. Best growth occurred in a 

 middle concentration — around seven or eight percent. When 

 tubercle bacilli are first set out upon fresh ground there is con- 

 siderable delay before new growth begins. The "lag" takes 

 days. Wherry explained the matter. Not until "both oxygen 

 and carbonic acid gas pressures reach an optimal point, does 

 growth start." 



Wherry had announced a law. He had, moreover, been 

 working with an "acid-fast" microorganism. How he was to 

 apply his new-found knowledge to make another acid- fast 

 organism grow (the bacillus of leprosy) never before culti- 

 vated on laboratory media, we shall discover later. 



Two months after the appearance of these studies, Wherry 

 sent a further paper to Hektoen. Four and a half pages were 

 headed, Cultures of a leptothrix from a case of Pari7iaud's con- 

 junctivitis [62]. The title needs inspection. Superficially 



