INFECTION AND DISINFECTION. 767 



and that the disease may thus spread ad infinitum. This capacity of 

 propagation, the possession of which is as certain as anything can pos- 

 sibly be, suggests the inquiry as to the manner in which the original 

 patient of our series became infected. He in his turn must have taken 

 the disease from some one else, but it is quite possible that he has never 

 been within a mile of a scarlet-fever patient. In many such instances 

 it is impossible to get any clew to the original case, but it sometimes 

 happens that evidence is forthcoming to the effect that days or weeks, 

 or even months before, a person convalescent from the disease has 

 occupied a room of which our patient was afterward a tenant, or that 

 some article of clothing which once belonged to patient number one 

 has been handled or worn by the person whose case we are considering. 

 It is evident that there must often be great difficulties in prosecuting 

 such an inquiry. 



Let us now take an example of a non-infectious disease, and notice 

 how it contrasts with the one we have just described. A young adult, 

 previously in good health, becomes sensible of a feeling of heat, alter- 

 nating with chilliness, and perhaps shivering, and slight pains in the 

 limbs. In a day or two there is more or less fever and thirst, and 

 some of the larger joints are swollen and very painful, while the skin 

 covering them is much reddened. The pain and fever are the princi- 

 pal symptoms ; but there are often others, a description of which is 

 unnecessary for our present purpose. The complaint lasts an indefinite 

 time, but, even in the absence of treatment, usually subsides within 

 six weeks. Such, in a very few words, is the course of rheumatic fever 

 or acute rheumatism. 



These two diseases, scarlet fever and rheumatic fever, have much 

 in common, but there are sharp points of difference between tbem. In 

 both fever is a prominent symptom, and, in addition to the display of 

 local symptoms, the whole system is evidently affected. The differ- 

 ences, however, are still more important. Scarlet fever is eminently 

 infectious. The air which surrounds the patient becomes contami- 

 nated and highly charged with the poison, and persons breathing it 

 run great risk of becoming affected. In a case of rheumatic fever, 

 although the secretion from the skin is generally very copious and 

 peculiar in character, so that the sense of smell is strongly appealed to, 

 there is no such risk ; the disease can not be conveyed from the patient 

 to those around him, however close the attendance and however defect- 

 ive the ventilation of the room. Infection from a previous case is, 

 therefore, never thought of in connection with rheumatic fever, though 

 the actual nature of the poison which causes the disease is as yet un- 

 known. The attack is often excited by exposure to cold and wet, cir- 

 cumstances which play no part in the causation Of scarlet fever. There 

 is at least one more important difference between the two diseases : 

 scarlet fever very rarely, indeed, occurs a second time in the same 

 patient, and the symptoms never become chronic ; rheumatic fever, on 



