n 



How is it transmitted V may next be aslced. Through the agency of the 

 dust we inhale, is tlie answer. 



A short time ago we spolie of infective matter; this infective matter is 

 the seed, placed in the dust by persons who have colds. 



Now, this is all theory, some will exclaim. Let us admit it is a theory. 

 Now, a theory is of value if it explains phenomena and in proportion as it 

 explains it liecomes a true theory; moreover, a Avorking theory has value 

 in enabling us to predict. 



Let me cite a few instances or examples and see how this infective 

 dust theory, if you choose to call it so, woi-ks out. 



Men who in towns are constantly nttiicted with colds and catarrhs, 

 with pains and aches in the joints, and with headaches, are often singu- 

 larly free from these complaints while in the country for an extended 

 period. It is true that mode of life has something to do with this; the 

 exercise, the plain food, etc., all contribute to their well-being, but one 

 factor stands out aliove all others— the pure atmosphere with the absence 

 of infective dust. 



It has long been noticed by those susceptible to colds that a cold often 

 follows a ride on the railway, and it is usually ascribed to some draught — 

 to some open window or door. In reality it is due to the highly con- 

 taminated air of the car— the aisles at times resemble in filthiness the 

 habitation of some domestic animal. 



Since interurban cars have come into use a new phase of this question 

 of railway colds, so to speak, has developed. ' The open car furnishes an 

 abundance of fresh air while the closed one in the Aviuter season may not 

 differ greatly from the steam road cars in regard to the polluted atmos- 

 phere. Svisceptible persons have often been puzzled hoAV they catch cold 

 0:1 a closed car on a comparatively warm day and do not catch cold in an 

 open car on a cold, raAv day, saj- in the fall Isefore the open cars are taken 

 off. The one is all di aught and the other has practically no draught. The 

 discerning individual will readily see that the air of one is pure, while 

 tliat of the other is not. 



Individual susceptibility of ( ourse varies greatly. Some persons seem 

 almost immune, or succumb only after an unusual exposure; the attack 

 itself may be slight or severe. 



Some men habitually employed in situations with infected dust seem 

 almost immune. Railroad passenger conductors are usually the picture 

 of health. This is easily explained: it is simply the action of the law of 



