pure cultivations are of very common occurrence, even in the 

 hands of those who are best fitted to carry on experiments of 

 this kind." 



So !far I have referred to some of the means by which we 

 are protected against the attacks of the very virulent micro- 

 organisms whose power under conditions favourable to their 

 multiplication is so. enormous. I might, if time permitted, refer 

 to other circumstances which exercise a protective influence 

 against these and other diseases the bacilli of which are in some 

 cases, like those mentioned, anoerobic, and in others are cerobic, 

 living only where they can obtain a supply of oxygen. The 

 bacillus tuberculosis belongs to the latter class ; human subjects 

 and many of our domesticated animals are liable to its often 

 fatal attacks, and it is commonly contended that the bacillus 

 which is the rausd causans of human tuberculosis is identical with 

 that which attacks cattle and other animals. To ascertain the 

 truth or otherwise of this contention was one of the motives 

 which led me to inquire more particularly into what has proved 

 an exceptionally interesting study. In my own experience I had 

 found nothing to justify the belief that human subjects could 

 contract the disease by contagion or infection in any form from 

 the lower order of animals, and I had known innumeral)le cases 

 where the opportunity to do so was afforded, no precautions 

 whatever being taken against it because no danger was suspected. 

 Notwithstanding the undoubted character and special ability, 

 therefore, of some of the scientists who insisted upon the identity 

 of the disease in all cases, I freely admit my St. Thomas-like 

 want of faith. Either the disease could not be contracted from 

 domestic animals, or else the natural protection against it was 

 so nearly perfect that the danger was practically removed by 

 agencies which operated without our knowledge. After much 

 careful reading with the object in view which I have already in- 

 dicated, I have been able to arrive at what I believe to be fairly 

 reliable conclusions on several of the most important points, and 

 these conclusions are most reassuring. First, with respect tO' 

 the identity or otherwise of the disease ; and here I refer to 

 Woodhead because, having had a long special training as Director 

 of the Laboratories of the conjoint Board of the Royal Colleges of 

 Physicians (Lond.) and Surgeons (Eng.), and having for some 



