272 HOW WE FIGHT BACTERIAL DISEASES 



into the blood when these bacteria die. When any protein sub- 

 stance decays, it breaks down into simpler substances, as in diges- 

 tion in our body. Some of these simpler proteins are poisonous 

 and are called ptomaines (t5'ma-inz ; Gr. ptoma, dead body). 

 Ptomaine poisoning, while not so common as was once thought, 

 often causes discomfort and even death. Two other kinds of 

 protein poisoning have recently been discovered, one caused by 

 certain foods which produce eczema and other skin diseases, and 

 another caused by the pollens of weeds, trees, or grasses and other 

 foreign proteins, such as particles of feathers of geese and chickens, 

 or hair from dogs, cats, horses, and other animals. Snake venoms 

 are yet another example of poisonous proteins. 



All toxins, when they enter the human body, cause the body 

 cells to react to the poison. If the cells are able to manufacture 

 antibodies rapidly enough to counteract the work of the bacteria or 

 their poisons, we recover from the disease. In such a case as this, 

 the body cells do the work in fighting the disease and the immunity 

 thus acquired is said to be active. In case the body cells themselves 

 do not work, and, instead, an antitoxin is used, which is manufac- 

 tured outside the body, we have an example of passive immunity. 

 Let us consider the latter case first, as it is easier to understand. 



Passive Immunity. — An example of passive immunity is that ob- 

 tained by the antitoxin treatment for diphtheria. This treatment, 

 as the name denotes, is a method of neutralizing the toxin caused 

 by the bacteria in the system. It was discovered by a German, 

 Von Behring, that the serum of the blood of an animal immune to 

 diphtheria is capable of neutralizing the poison produced by the 

 diphtheria-causing bacteria. Horses develop large quantities of 

 antitoxin when given the diphtheria toxin in gradually increasing 

 doses. The serum of the blood of these horses is then carefully 

 prepared and is used to inoculate the patient suffering from or 

 exposed to diphtheria, and thus the disease is checked or prevented 

 altogether. The laboratories of boards of health prepare this 

 antitoxin and supply it fresh for public use. 



It has been found from experience in hospitals that deaths from 

 diphtheria are largely preventable by the early use of antitoxin. 

 It is therefore advisable, in a suspected case of diphtheria, to have 

 antitoxin used at once. 



