72 



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

 dust we inhale, is the answer. 



A short time ago we spoke 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 becomes 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 clioose to call it so. woi-ks out. 



:^Ien who in towns are constantly afflicted 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 above all others— the pure atmosi)here 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 aisl(>s at times resemble in filthiness the 

 habitation of some domestic animal. 



Since interurb.-ni cars have come into use a new phase of this (juestion 

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

 al)undance of fresh air while the closed one in the winter season may not 

 dilfer greatly from th? steam road cars in regard to the polluted atmos- 

 phere. Susceptible persons have often been puzzled how they catch cold 

 o:! a closed car on a cinnparatively warm day and do net catch cold in an 

 open car <ni a cold, raw day. say in the fall l;efore the open cars are taken 

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

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

 that of the other is not. 



Individual susceptibility of course 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 simi)]y the action of the law of 



