278 THE HUMAN BODY 



into the blood. Successful combating of such diseases requires 

 only that the toxin be neutralized. In course of time the bacteria 

 will reach the end of their development and die. 



The antitoxin for any particular kind of toxin will neutralize 

 it whether produced in the body which is infected or in some 

 other body from which it is transferred to the infected one. This 

 fact has made possible the development of the well-known anti- 

 toxin treatment. Animals, usually horses, receive doses of toxin 

 obtained by growing the bacteria on culture media in proper 

 vessels. These doses are small at first, but are gradually increased 

 as the animal acquires immunity. In course of time the blood of 

 an animal so treated contains large quantities of antitoxin. Con- 

 siderable amounts of blood can be withdrawn from animals the 

 size of horses without their suffering the slightest inconvenience. 

 It is thus possible to obtain abundant supplies of antitoxin. 



The methods of purifying antitoxin-containing solutions are 

 so perfect at the present time that no one should feel the least 

 hesitation at the prospect of its use. The percentage of deaths 

 from diphtheria has fallen from more than fifty to about two 

 since its introduction. The distressing symptoms which some- 

 times follow its administration are not effects of the antitoxin, 

 but are due to imperfect neutralization of the toxin, and appear 

 because the life of the patient, thanks to the partial overcoming 

 of the poison, is saved long enough to give them time to become 

 manifest. 



Protective Inoculation. It has been found practicable in some 

 diseases, notably smallpox, to develop immunity by infecting the 

 Body with an organism which is not virulent enough to endanger 

 life but which produces immune substances that protect the Body 

 against the more virulent infection. On account of the specific 

 character of immunity this method can only be used where vir- 

 tually the same organism occurs in virulent and non-virulent 

 forms. 



The most hopeful path of progress at present toward the mas- 

 tery of disease is along the lines here indicated. We may look 

 forward confidently to a time when most if not all the acute in- 

 fections will be brought under medical control through applica- 

 tion of the principles of immunity. 



The Coagulation of the Blood. When blood is first drawn 



