PEOFESSOR G. P. GIRDWOOD. 5 



ing the intnulor and repairing the breaoli. Directly the intruder appears, he is surrounded 

 by the leucocytes of the blood, which attach themselves to the intruder, and the phagocytes 

 devour him, thus preventing him from increase by propagation, and thereby rendering him 

 harmless. If the vitality of the individual be not sutHciently strong for this, the leucocytes 

 ■wall up the intruder and form the tubercles found in the lungs of persons affected with that 

 disease, and these undergo absorption, ami cicatrices are frequentl}^ found after death, proving 

 the natural cure of the disease. 



Here are some of the advances lately made in assisting to prolong hunum life, the 

 recognition of the cause of these diseases and the tracing out of tlie life-history of these 

 micro-organisms has led to the knowledge that these little bodies require material on which 

 to live, and which is generally known as " dirt or matter out of place," and hence to direct 

 sanitary arrangements, such as the filtration of water-supply, the various improvements in 

 building and ventilation and protection of houses from the incursions of these destroyers, 

 and hence the general improved sanitary conditions and the decrease of the death rate. 



In 1882 our esteemed and lamented first president of this section. Dr. T. Sterry Hunt, 

 addressed the section on the relation of the natural sciences. He would have been delighted 

 could he have seen the results now attained by the labours of the worshippers at the shrines 

 of the correlated natural sciences to which he devoted liis life. 



It has been said that "no great or comprehensive fact in science was ever established 

 without being preceded b}- a bold though sagacious conjecture. Hypothesis of some kind 

 or other is iiivariabl}- the i)recursor of truth." ' 



The theory mentioned aljove, and which was advanced some fifty 3'ears ago, that these 

 diseases were the result of a fermentative growth, and the facts now known about them, as 

 proved by the microscopist and the chemist, amply demonstrate the truth of this remark. 



Such proofs lead to a speculative turn of thought when explanation of observed facts is 

 required. As soon as a number of facts are observed tending in a certain direction, some 

 hypothesis is sought and given as an explanation or the cause of the facts. The action of 

 the leucocytes and phagocytes in respect of the presence of these micro-organisms suggests 

 the question : Why should these Ixidies so act? Why should these leucocytes and phago- 

 cytes be attracted to the intruder? Is it electrical attraction, or are they attracted by 

 molecular vibrations? The opinion that these movements are the result of molecular 

 vibrations is gaining ground. 



Molecular vibrations are taking place in all kinds of matter at all times, whether solid, 

 liquid or gaseous ; indeed, the difference in these states, solid, liquid or gas, is simply the 

 difference in the size and frequency of their vibrations. But besides these alterations in 

 physical state, it is found that many substances, such as chlorine, bromine and iodine, act 

 upon other bodies, such as antimonj', arsenic and iron, at ordinary temperatures ; but if 

 they be heated — that is, if the energy of molecular vibration be increased — we find chem- 

 ical action is more energetic, whilst oxygen and hydrogen, or chlorine and hydrogen, do 

 not comliine at ordinary temperatures in the dark. If, however, oxygen and hydrogen be 

 heated, chemical union takes place, and if hydrogen and chlorine be subjected to the action 

 of light, they combine uiuler its influence. If a mixture of nitrous oxide gas and the 

 vapvurs of bisuliihide of carlnju be subjected to the action of heat, they combine, and the 

 light therefrom is sufficient to induce the active union of hydrogen and chlorine, in the 



' " Library of Useful Knowledge," vol. xi., "Magnetism,' page 32. 



