IMMUNIZATION AND THERAPY. 243 



patient's toys, eating utensils, dishes, clothing, or bed-linen 

 may convey the disease. The infecting agent is the small 

 pieces of membrane coughed up by the patient. They may 

 be so small as to be invisible, and when they lodge on 

 the clothing of the nurse or physician, or on the furniture 

 or hangings in the room, they escape notice. When the 

 patient sneezes or coughs, a cloth saturated with bichloride 

 should be held before the face. Infection from this source 

 should be guarded against very carefully. 



It is very unwise, as well as dangerous, for the physician, 

 when examining the throat, to stand directly before the patient. 

 The examination usually induces a coughing spell or gagging 

 severe enough to detach small pieces of membrane, which 

 lodge on the clothing, hair, or beard of the physician. He 

 may escape the infection, but he serves as a walking incubator, 

 and any one coming in contact with him may become infected. 



It should be borne in mind that in many cases of diphtheria 

 the throat manifestations are very mild, and the disease may 

 not be suspected. For this reason it is advisable to regard 

 all cases of angina with suspicion until their identity has been 

 established. It has been suggested that the infection may be 

 conveyed through milk, although that mode would seem rather 

 improbable unless a piece of membrane was accidentally de- 

 posited in the milk. 



Cats may be a frequent source of infection. Their wan- 

 dering propensities predispose them to infection from any 

 case in the vicinity, and when a child plays with the cat it 

 may contract the disease. During diphtheria epidemics, or 

 when cases are known to exist in the immediate neighborhood, 

 it is well to watch these household pets carefully, and chil- 

 dren should not be allowed to play with them. 



The toxin of the diphtheria bacillus is intensely poisonous. 

 A toxalbumin has also been isolated. The chemical compo- 

 sition of the toxin is unknown. It is obtained by filtering 

 bouillon cultures through a porcelain filter. It is destroyed 

 in five minutes by boiling. When kept in a cold dark place 

 it retains its toxicity for years. 



Immunization and therapy : Behring was the first to dis- 

 cover that the blood-serum of animals immunized to diph- 



