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Bacterium welchii (Migula), or Bacillus aerogenes capsulatus (Welchj.was discovered in 1891 by Professor Welch in the blood and tissues of a tuberculous person who had died of hemorrhage from the rupture of an aortic aneurism. The entire body was emphysematous and distended with gas. Subsequently this bacillus has been isolated in many pathological conditions, among which may be mentioned emphysematous gangrene and gaseous phlegmons of various tissues following injuries, surgical operations (herniotomy, nephrectomy, urethrotomy, appendectomy, amputations, etc.), salt infusions, hypodermic injections, 'and cholelithiasis. It has also been found in emphysema of the fetus, puerperal eclampsia, physometra, emphysema of the uterine wall, puerperal gas sepsis, urethral stricture with cystitis, emphysema of the bladder, interstitial emphysema of the gastro-intestinal wall, pneumoperitonitis with or without perforation, pneumonia and pulmonary gangrene, and in meningitis. HerterI has suggested that certain anemias, especially in children, may be associated with a chronic invasion of the intestinal tract by B. welchii. In the light of the seeming increasing importance of B. welchii, it was deemed desirable to investigate the immunological relations of this bacterium.

von Pirquet I has recently made use of the local reactions sometimes elicited in individuals affected with infectious diseases when the toxin from the microSrganism causing the infection is i n j e c t e d into the body. He has applied the phenomenon to tubercular infections and has found that when tuberculin is introduced into the dermis that a local reaction results in tuberculous subjects and no reaction of any consequence in the non-tubercular. This local cutaneous reaction lasts at least eight days. yon Pirquet has applied this test in infants and children and finds that it is of diagnostic value especially in the beginning of the disease. Vall6e 2 has applied the cutaneous tuberculin test to cattle, horses and guinea-pigs. He finds that the reaction is positive in the majority of tuberculous animals and conversely does not occur in normal animals. It is not within the province of this paper to consider in detail the cutaneous reaction for tuberculosis. This subject will form the basis of a later communication. Calmette 3 has made use of the foregoing principle, but has modified the method of applying the test. He instills the tuberculin into the eye instead of into the skin. He finds in cases of tuberculosis, after six to sixteen hours, that the conjunctiva, particularly *