466 THE POPULAR SCIENCE MONTHLY. 



The more widely the nidus is diffused, the less likely is this to happen. 

 In small-pox, in scarlet fever, and in measles, the nidus is widely scat- 

 tered. In none of them is a germ likely to make the round of circulation 

 more than two or three times, without being conveyed to its nidus. 



In typhoid fever the nidus is situated in a limited portion of the 

 bowel, the sole route to which, by way of the circulation, is through 

 an artery the size of a crowquill ; a typhoid-germ may be taken in 

 through the lungs, and may make the round of circulation two or three 

 dozen times, without being likely to enter that particular vessel. The 

 more often this may occur, the greater the chance of its being thrown 

 off f ro.m the system without acting. But, if the typhoid-germ be taken 

 in through the digestive organs, it is brought into direct contact with 

 the seat of its nidus, and can scarcely fail to act. Hence the great 

 danger of drinking water or milk contaminated with the typhoid- 

 poison. 



The glands which constitute this nidus are not equally prominent 

 and active all through life. In infancy they are quite rudimentary. 

 At two or three they begin to grow, and gradually increase in size, 

 and presumably in functional activity, till the age of puberty. They 

 continue to be very distinct for twenty or twenty-five years. After 

 forty they begin to get less, and gradually diminish till at seventy they 

 have dwindled away so much that they can no longer exercise any 

 active function. Their period of prominence and of functional activity 

 corresponds exactly to the period of susceptibility to the action of the 

 poison of typhoid fever. That disease is extremely rare in infancy ; 

 from two to six, or seven, it is more common, but is generally very 

 mild. At fifteen or sixteen commences the period of greatest liability 

 to it ; and from that age until thirty-five and forty it is very common 

 and very fatal. After forty -five it begins to decline both in frequency 

 and severity ; and goes on declining as years advance, till at seventy 

 the liability to it may be regarded as practically worn out. When it 

 occurs in advanced life it is generally mild ; but its occurrence then is 

 as rare as in infancy. Increased and diminished susceptibility to the 

 action of the poison of typhoid fever correspond exactly to the in- 

 crease and diminution in the size and functional activity of the glands 

 which constitute its nidus. 



The insusceptibility to the action of the poison, which is naturally 

 and slowly developed in old age, is artificially and rapidly produced 

 by the destruction of the nidus during an attack of the disease. 



Using the word contagious in its proper sense of communicable by 

 contact, and regarding the typhoid-poison as a parasite whose nidus is 

 in the glands of the bowel, we are led to the conclusion that the disease 

 to which it gives rise, though undoubtedly infectious, can scarcely be 

 contagious. We know from our experience that it is not so ; for it 

 never spreads in hospitals, and attendants on the sick suffer no more 

 than other people. 



