Some Points in the Life-history of Bacteria. 131 



up certain changes -which are known by the name of tubercle. 

 Now, although the tubercle bacillus is so slow of growth, and 

 does not readily gain a footing, it is very tenacious of its powers 

 of vitality. This is partly due to its formation of spores. The 

 expectorations of consumptives are infectious even after drying. 

 It is recognised that phthisis is apt to cling to certain houses, 

 and one need not wonder that it should if one considers the dirty 

 habits of some of the inhabitants — of some even who would be 

 surprised if charged with being dirty. Yet the extensive use of 

 hea^^ hangings and thick-piled carpets, though eminently re- 

 spectable, is essentially dirty. Consumptive patients should be 

 taught to spit into water, or into some substitute for pocket- 

 handkerchiefs which can soon be burnt. Cattle are very prone 

 to tuberculosis — it appears to be increasingly so — and there is a 

 very general inference that the flesh and milk of affected beasts 

 should not be used. The milk appears to me to be a greater source 

 of danger than the meat, for the latter is not taken raw, while milk 

 is commonly so taken ; moreover, the tuberculosis is an affection 

 of lungs, glands, and serous surfaces, and easily recognised. But 

 I am sceptical myself if tuberculosis is at all frequently inocu- 

 lated in this way. Consumption of the lungs, far and away the 

 most important among tubercular diseases, is certainly not got 

 by feeding. There remain abdominal tubercle and more or less 

 generalised tuberculosis to be accounted for, and it seems to me 

 that the chain of cause and effect here is with extreme rarity 

 complete. A point of interest is that out of the vast number of 

 people who are exposed to tubercular infection, a comparatively 

 small number develop the disease ; the bacilli cannot get a 

 footing. There is a struggle going on between the tissues and 

 the organisms for mastery. When the tissues are in a healthy 

 and vigorous condition they are better able to combat the bacilli. 

 On the other hand, when the bacilli can find, particularly in the 

 lungs, a resting-place where they can grow for a while and thus 

 muster their forces, possibly secreting some compound which 

 depresses the vitality of the surrounding tissues, they have a 

 better chance of presently carrying on a successful invasion of 

 the same. Light kills the bacilli. If the belief of some is true, 

 that the bacillus has a non-parasitic phase of life, then the value 

 of light in and about dwellings is extremely great. 



Immunity. — This subject is still very much in the workshops. 

 We are only able to see the seamy side, and there is much ap- 

 parent confusion. We all know that in most infectious diseases 

 one attack more or less protects from a subsequent one. It 

 is very easy to theorise about this, but very hard to find the 

 key to it. One notion was that the microbes used up some- 

 thing in the system, and that the system never, or only after a 

 longer or shorter interval, was able to make up this lost factor. 



